Dfyjkt

Pick one.

Humans are very adaptable creatures. With the right plotline preparations or luck you can reasonably pitch a subset of humanity surviving pretty much anything.

Supervolcano? Some hardy folks who’ve been stockpiling tins survive.

Nuclear war? Some hardy military types in bunkers survive.

Deadly plague? Some hardy people with natural immunity survive.

From the point of ‘humans survived’ it’s very easy to come up with all sorts of reasons they might not have all the pre-disaster knowledge, ranging from ‘the experts on that subject are dead’ through to ‘the disease gave every survivor amnesia’.

As the author here you have an awful lot of power to pitch anything as plausible, though I would caution against events that completely strip the atmosphere or boil the seas, you can plausibly get away with a handful of people surviving an awful lot of disasters.

As some comments have already mentioned, I think what you're asking for is unfeasible as stated. Here's my try though:

Double Whammy

An unexpected solar flare throws a massive burst of EMP at the Earth, frying virtually all electronic systems. Some people die immediately, but comparatively few. All lines of communication and supply lines in turn get severed. It's starvation that claims the vast majority of the casualties caused directly by the Great Catastrophe.

Couple that with a wave of mass anti-technology hysteria, possibly but not necessarily religious in nature. The survivors are convinced that technological advances themselves are the cause of humanity's predicament. Thus mankind sets about destroying hardware and software alike, as well as physical records like books.

However that still leaves the knowledge carried in human minds. With nearly unanimous worldwide agreement, all the various fragments of society hunt down and kill scientists, teachers, engineers; in other words purveyors of knowledge and the 'educated elite'. This gives rise to what can be called a spontaneous Khmer Rouge 2.0. Mankind considers knowledge to be evil and turn their backs on it, so that whatever fragments remain cannot be spread and are doomed to die with the people carrying them.

EDIT: For those unaware of the history behind the Khmer Rouge, here's a handy link: Khmer Rouge genocide

Adult Killing virus

Whether intentional or accidental, a virus is released that is almost entirely lethal for adults. You can of course adjust the numbers, but most people don't survive puberty, and even amongst those who do, at least initially suviving to adulthood is no guarantee. This will lead to young teen agers and tweens being the most knowledgeable people. Of the few who do survive, their children are more resistant to the virus.

Initially infrastructure would fall apart, electricity and running water would become exceedingly rare. The kids in agrarian/low tech communities would likely do better already being slightly more familiar with the necessities of survival than those in urban environments. While not all knowledge would be lost, most of it would be inaccessible... and if it takes 3-4 generations for the majority of the population to become resistant to the virus, well most people will be more concerned with day to day survival than digging through books to learn about what might be possible.

There are a number of primitive people left on Earth with virtually no contact to the outside world. A plague, virus or nano-tech attack that spreads between humans (and starts its outbreak in several places at once in order to make quarantines ineffective) might well spare one or two of those, and they would indeed have no link to previous (our) civilisation on Earth. Genetically, however, they would be very closely related.

Whatever artifacts, devices and writing are left once the rest of humanity is gone would be unintelligeble to them (many of them don't even have a written language, so they wouldn't even know enough to start translating). By the time their civilisation has reached more modern times - easily thousands of years - not much will be left. The life expectancy of our modern storage mediums is laughable. Everything electronic will be gone. Almost all paper will be gone. Some monuments and other stone inscriptions will be all that is left.

A virus affecting brain (memory)

It doesn't have to kill (or immediately kill) but causes a sort of dementia, affecting what those infected remember.

Once you can no longer prepare food, you can still survive responding to instincts (so your body still has the ability to recognize e.g. what is edible).

Over one/few generations the organisms of people will eventually learn to fight down the virus and become immune to it but during that time there was only very limited (to none) knowledge passed between generations. You may have small isolated groups of people with specific knowledge survive if you need to, to later train others to some degree. You can also wipe all the knowledge (even languages) completely, making it entirely start from the beginning. Up to you.

You can go with a black plague on hormones: a pandemic killing on average 90% of the world population, with higher death rates in the most advanced regions.

The remaining survivors will be sparse and most likely ignorant on how to manage modern infrastructures (take a shepherd of the Masai Mara, and put him in the control room of a 3rd generation nuclear power plant, or a surgeon in LA dealing with the back end of an online shop), resulting in them rapidly crumbling down.

Humanity will likely restart, but knowledge on what those things were will quickly fade into legends.

There are lots of good answers already about how to knock out our technology (I was going to go with gigantic solar flare but @nullpointer beat me to it). Therefore I'm going to just address the second point - how to make sure we become technological illiterates. My answer there is very simple: you don't have to do anything other than let a catastrophe happen.

Personally, I'm a firm believer that our entire way of life and everything we know and do is built on a flimsy house of cards. Once a serious enough event happens that stops regular deliveries to grocery stores, at least 50% of everyone living in industrialized nations will be dead in just a couple months (the death toll will probably be more than that, but I'm being conservative). Once that happens it is all downhill from there.

CPU construction, computer building, machine shop working, power plants, and even modern farms all rely upon extremely specialized equipment and knowledge, to the extent that almost no one has the capability to do anything on their own. There is not a single person out there that could build a CPU if they needed to. Once the "CPU factories" stop working, that is the end of computers. There is no one out there that could build a car, or even a single part for a modern car engine or transmission - not without a factory, which will be shutdown in weeks and unusable not too long there after. You can't just walk up to a shut-down oil refinery, hit a button, and start collecting gasoline. Even if you could you won't be receiving anymore shipments of crude oil to process. Too bad too, because with all the easy-to-find crude oil already pulled out of the ground, you have exactly zero chances of getting anymore. You certainly aren't going to travel out to the nearest off shore oil-rig and pull some more crude oil out of the ocean floor.

Without the infrastructure that we rely on every single day, most of our modern technology will be useless in just a couple years (if even that long). There will probably be a few people who survive the mass starvation that will follow any serious "Apocalypse" who can keep some semblance of technology running for maybe a decade. After even just one generation though that will all be gone and we will be back to the basics - subsistence farming, with perhaps and easy transition into the iron age thanks to all the metal we leave everywhere. It doesn't matter how many encyclopedias are left lying around because any that aren't burned for heat (cold climates) or ruined by moisture and mold (warm climates) are going to be effectively useless in a generation because the lack of modern schooling and basic exposure to modern technology that we take for granted is necessary to even understand the basic concepts in them. As someone who is very technologically proficient and has advanced degrees in physics, an encyclopedia explaining the details of an internal combustion engine will not make me anymore capable of designing and building one.

To summarize

The details of the disaster don't really matter. Anything that disrupts modern life sufficiently to stop a few shipments to grocery stores will turn the house-of-cards our infrastructure is built on into a smoldering ruin in no time. Starvation will lead to an irreversible collapse of infrastructure and the fact that the "new" world will require a completely different set of skills to survive will cause humanity to effectively lose all of its knowledge of modern technology/science in no more than a generation.

One option would the Horizon: Zero Dawn option.

Your precursor humanity had a plan for the apocalypse:

A series of Deep bunkers and facilities worldwide which have the equipment to produce babies in vats and raise them enough to release into the wild. The technologies are all so insanely advanced that they're regarded as magic by the people they produce.

Perhaps it was intended to produce soldiers for post-armageddon warfare, perhaps it was purely humanitarian. Regardless, the level of education provided is insufficient to build or maintain pre-apocalypse technologies, so they revert to tribalism and the Precursors fade into the mists of time soon after the cloning facility shuts down.

This way it doesn't really matter how badly the apocalypse messed up the planet, as long as the air is breathable and the land arable humanity can start again, perhaps after a thousand false-starts. It doesn't matter if the people die, another batch will be grown and sent out to pick up where they left off until humanity takes off again.

The only people disconnected from modern-day technology / society are remote, isolated tribes in South African rain forests, African bush, and maybe some Aboriginal tribes in Australia.

The number of ELE's (Extinction Level Events) are numerous (as folks have pointed out). But, having someone stumble across the wiped-out civilization as if it's alien / foreign to them requires them not knowing about it in the first place. And that requires isolation from that civilization in the first place.

You have your pick of ELE's.. neutron bombs can wipe out organic matter in a populated area while keeping the ruins intact. A virus can wipe out a lot of people, but not isolated tribes due to not being able to bridge the gap without exposure from outside source. etc, etc.

The problem here is that even these isolated tribes have often had some outside contact as anthropologists / researchers have gone around trying to catalog everyone on the planet. Some tribes will have occasional trade, so you can walk into a remote village and see people with modern t-shirts on, or carrying a rifle. And even tribes that want nothing to do with the outside world will still have been visited by a researcher here and there that acts like an ambassador, but the researcher respects the tribe's wishes and doesn't taint them with modern technology.

That would be your best bet.. just a remote tribe of people that didn't progress with the rest of the world, because they liked how they lived and wanted to keep it that way.

Here's some options...

Small group of Native Americans that got sick of modern society, and how modern Native Americans have fallen in with it with casinos and such. So, the small group isolates themselves deep in the reservations away from everyone else for several generations. Sort of like M. Night's "The Village", the parents make a vow to never speak about the outside world, and raise the kids with the "old ways". The parents may have had contact with the outside world occasionally, but contact stopped, and they just figured the outside world forgot about them. Then one of the kids grows up and gets bold and starts exploring after the elders start passing away.. and stumbles across ruins of the former world... vast cities desolate and no clue what happened. No idea what most of the technology they see does.

You can do this with a South American rain forest tribe.. or an African river tribe.

I think Aboriginal and Inuit (Eskimo) tribes are pretty well indoctrinated into modern society even though they choose to live with the old ways sometimes. So, they may be off the table as ones to pull this scenario on.

Hope this helps.

TL;DR

Make it so there are few enough available tools and few enough people that they cannot properly use the tools to make a quick comeback, and reduce the population and communication enough to stifle the preservation and spread of knowledge.

Even then, the knowledge loss might not be as severe as you specified, as it is difficult to stamp out all knowledge of something completely. This is evidenced by actual history and knowledge that has been preserved for thousands of years.

Full Answer

To start, let's examine the two opposing requirements one at a time and specify a limit to either exceed or not surpass...

1. human will not go extinct

Basically, all this means is that you need to limit the severity of the event. Almost anything can work as long as it is in moderation. Even a supernova would work as long as it was far enough to limit the damage to just the right amount.

2. a catastrophe on the right scale that can wipe out the current civilization [...] will start to thrive again after some time has passed, but should not have any knowledge of the just-wiped-out civilization except some relics/artifacts and ruins, kind of like how we look at ancient civilizations

For this, you need to at least destroy enough of our infrastructure that nobody who wants to find the necessary tools can find them, and reduce the population enough that there are extremely few people left who know how to rebuild.

The first part, making sure there is no extinction, is the easy part: all you have to do as the author is say "but it was not so bad that humans went extinct." So I will concentrate on this second part. Also, since you could easily say "magic," or "aliens take over," or "virus makes people dumb," or "new supreme world ruler does it through his evil scheme," or similar, I won't bother with those author-fiat methods... if you use them then just say "just because."

To oversimplify the matter, you need 3 things to sustain the society and technology: tools, knowledge, and people.

Tools

To make the vast majority of objects that we take for granted, special tools are needed. I worded the previous sentence the way I did so that it can omit objects and tools that can be created by stone age technology. These special tools are often difficult to create and require special tools to create, which often require special tools to create... modern technology is built upon the technology of yester-year, which is built upon....

This might seem like a shaky tower of technology and make you wonder how we keep it going, but all it takes is 1 or 2 of these special tools to remain in the hands of someone who knows how to use it and many of the other tools can be rebuilt. All it takes is 1 wood or metal working mill or 1 lathe to remain in the hands of someone who knows how to use it (or figures out how to use it), and with that most of the other tools can be remade and modern technology cannot be forgotten. So the destruction of these tools needs to be complete enough that they are not available to anyone with the right skills.

Knowledge

To get to the point you are looking for, nobody with the knowledge of how to retain modern technology can be in a position to do so, and/or they cannot be in a position that allows them to pass that knowledge on.

Enough generations need to pass in this condition to thoroughly wreck their knowledge base. At the very least, there can be nobody left with the original knowledge; that is, enough time passed that all original survivors are gone. Further, it would probably require that everyone who could have talked to the original survivors are also gone; that is, originals gone and everyone they could have talked to is gone. If there is so much as a 10 year old kid who knows how to use a lathe or mill or who knows other useful tech-preserving information, and if that kid could live to 80 or 100, then that's 70 to 90 years before the kid is gone, and another 70 to 90 years before any 10 year old kids who he passed his knowledge to are gone. That is at least 150 to 200 years before all knowledge is third-hand knowledge and therefore of drastically reduced use. This also means that the vast majority of knowledge about civilized life and previous social structure is now gone too... people still remember that there used to be a France, a Russia, a United States of America, etc., but those concepts are something that the kids of that time don't care much about and have no use for.

All it takes is a group large enough and prosperous enough to support a couple of thinkers and allow them to devote their time to discovery and invention for a comeback to start happening. So, in order to thoroughly oppress their knowledge to the point you requested, the event needs to keep their living conditions terrible for quite a while so that preserving or relearning knowledge is not a priority.

Even after all this, assuming you keep it at all realistic, there will still be people passing on tales of times past, including vague descriptions of devices used such as giant synthetic bird vehicles and carriages that drive themselves, etc., and maybe even references to the long lost cultures and nations centuries or millennia away. It would be very difficult to stamp out this knowledge completely and entirely, but you asked for "like we look at ancient civilizations," so that's ok since the major civilizations of history were already known before we discovered their remains.

People

Saying that people are necessary sounds obvious, but it is not just a mere presence of people. For civilization and technology to thrive, a critical mass of people is required. That is, there has to be so many people that those people are able to share knowledge and ideas, to teach each other.

Another aspect of this is that, if there are enough initial survivors, then someone somewhere with the knowledge to preserve and rekindle technology is going to stumble upon the tools they need to do it.

So you need to have few enough survivors that they cannot create a free-flow of knowledge around the region, much less the world, and few enough that you don't have knowledgeable people finding the tools they need.

You will probably need to keep the population reduced to small pockets of people, most of whom don't travel much (to limit communication), for at least the first 150-200 years mentioned previously.

Commentary

Something you need to keep in mind is that some people are very resourceful, some are very prepared, and some are both prepared and resourceful.

There are still people today, even in industrialized modern society, who are still practitioners of ancient technology, all the way back to stone age. There are people, and I know some of them, who can leave town with nothing (literally nothing... they could go naked if they had to) and feed themselves and start making old fashioned tools. Some of these people even have metal-working smelting and smithing knowledge. No matter what catastrophe happens, if it leaves even just a few of these people on the planet then you are unlikely to lose all social and technical capability, as they would immediately be right back up to at least stone age, possibly iron age capability.

There are also people who hoard stashes of food, resources, and knowledge. These people are often called "preppers". Both private groups of people and also national governments are prepped for major catastrophe. If you watch (and believe what they say) some of the prepper shows, some of those people have enough supplies stored to last well after they die of old age, and their supplies will continue to be used by future generations. Some of these include methods of renewable electric generation and tools for rebuilding after a catastrophe.

And if that weren't enough, there are literally books about rebuilding civilization after a catastrophe, condensing human knowledge into a form that can be readily used for that purpose. I happen to have two copies of such a book, which covers everything from agriculture to engines and electricity, and many things in between, including stepping stones to get back up to that level. It even includes many shortcut technologies that would allow us to skip over technologies that existed in the past and instead jump straight back into (or closer to) the end-game of nearly modern technology.

So you need to get rid of people skills, get rid of tools, and get rid of books. And not just the "how to rebuild civilization after a catastrophe" kind of books I just mentioned. For what you asked for, you need to get rid of all the history books, school books, and basically practically every other book that could talk about nations, technologies, or anything else you say should not be known. This is a tall order.

This, combined with the high availability of resources to be scavenged from the dead husk of the previous civilization means that this will be a difficult task and the event needs to be so very deadly and violent that it kills and destroys practically everyone and everything, leaving only a tiny remnant of humanity and without tools.

Also, the catastrophe needs to come as a surprise and happen swiftly so that people cannot prepare for it. If you know a year ahead of time, or maybe even just months, then the governments might push hard to put a "civilization jump-start package" space craft into orbit, either with a crew to bring it back down later or with an automated landing system. If individuals have time to prepare, they will do lots of things; hoarding resources, but possibly also burying them, putting some out to sea, flying some in planes or balloons...

So it needs to be swift and it needs to be a surprise. Even then, if more than just a few people survive and with a few tools, it will be hard to suppress the tech and social bounce back and to destroy the knowledge.

Real world example

There are historical examples of people cut off from others who have retained historical knowledge in one form or another, even if not very useful, for long periods of time. One of the better examples is probably the native Americans who thought that one day people would come across the water. They may not have had any realistic ideas about the true nature of where their legend came from, but it seems reasonable that their legend could have come from scraps of history passed down through the ages.

One of the things you will have to figure out how to deal with is the fact that people are actively trying to preserve their knowledge. We still find written records from thousands of years ago, and some cultures have traditional oral records which they teach to the next generation and take great pains to keep intact as much as possible. These records allow knowledge to skip ahead many generations, even thousands of years.

And now, what I consider to be the very best example, especially for you since it even involves a similar catastrophe...

There is a recorded event in Earth's history that, as recorded, is just about the worst catastrophe that could happen and leave humans to repopulate. This catastrophe is often referred to as the great flood, or Noah's flood.

The Abrahamic religions (Judaism, Islam, and Christianity being the most widely known and held Abrahamic religions) all stem from the person Abraham, who lived 10 generations after the catastrophe.

Whether or not you religiously believe the texts of the Abrahamic religions, there is no doubt that the written records that they kept are valuable and, so far for the events that we have found significant evidence to weigh it against, accurate accounts of history. Time and time again, when all the evidence is in for any given historic or archaeological inquiry, these records have been shown to be historically accurate and valuable tools for archaeology. And these written records indicate that there was a major world-wide flood which devastated the planet and left only a small handful of people alive. This major flood itself is still under debate as to whether or not it happened, but millions of people believe that it did.

Not only did humanity bounce back from that catastrophe, but we even have the catastrophic event itself documented, including its duration, the people that survived, how they survived, and an overview of the repopulation of the planet.

Further, we still have preserved knowledge of the people who lived before that catastrophe. In fact, we have names of people, at least 1 city, the occupations of some people, including an iron worker, and a very brief and high-level description of the overall state of affairs of humanity at that time: that it was bad, people were evil, and society was likely much worse than it is today.

Whether or not you believe this catastrophe account personally, you are looking for something believable. Millions of people do believe this account, meaning that it must be considered believable and therefor provides an excellent sample of a believable catastrophe.

An alternative

Alternatively, if you are willing to change the landscape and living dynamic of the world, then you can work against the things I mentioned above by using your world-building against them.

For example, if the planet conditions are so harsh after the catastrophe that people are forced to spend all of their time farming with little yield just to eat enough to barely sustain themselves, and if all the forests were burned down (say, during a huge solar event) leaving little fuel to use for technological uses, that could greatly stagnate the progress and cause it to fizzle out.

Even so, I think the governmental massively prepared survival compounds would persevere, at least one of them. So at that point you probably need to combine all this with the idea someone else mentioned of a secondary event to kick them while they are down. But even then, if the story of Noah (and those with him) and the great flood is any indicator, the knowledge might not be as completely lost as you want.

I’m surprised nobody has suggested this:
A virulent nanobot infestation that attacks all processed metals/plastics/inks/take your pick - specifically the ‘grey goo’ type

Survivors on a space ship. A few years in the future it’s possible to put humans in stasis. This is used to send humans to Mars or somewhere else. Some global catastrophe wipes out all humanity except the individuals in stasis in space.

They wake up a few thousand years later because the ship’s fusion reactor is running out of fuel. Unfortunately all the knowledge is stored on the central ship computer (or not even there but only on Earth) and they can’t take it with them in their landing pod.

So all they can teach to their children is what they remember. I expect the astronauts to have good knowledge in things like advanced engineering, programming and aviation (which would all be pretty useless in a post-apocalyptic world) but apart from that they can pretty much only teach basic high school knowledge: Reading, writing, a solid foundation of mathematics and physics, rough history (how many names and years do you actually remember?) and biology.

What if only a few kids below reading age survived a virus attacking more evolved brains. The less you want to be known, the lower you set the age of survivors. The virus dies out with their hosts (somehow).

Books and paper will still exists. And even without knowledge of current languages, and with all electricity and batteries gone, it might still be just a matter of time before the smartest ones and widest travelers manage to decipher and read our languages. With the help of children's books first. Pictures and simple words. In the beginning, those few readers might become extremely powerful as they fast forwards through technological development. Just having the knowledge of what is physically possible is a boost to that.

The internet shuts down itself.

Part of the story in the move Transcendence was when the singularity is achieved by the protagonist but the rest of his research team forced him to "kill himself."

Given our constant need to connect to every convenience device we've ever consumerized, all earthly civilizations won't last a day when the internet suddenly was gone. A global digital blackout will rewind humanity to at least a few decades.

How?

Somehow the singularity occurred, without precedence. The big players in the AI Industry investing billions on optimizing production efficiency, the lowkey AI hobbyists and hackers playing around with code, the regular web surfers ever-expanding the data volume of humanity, along with the inherent inconsequential non-events unaccounted for, all interconnected, and all culminated to the awakening of an entity that far exceeds the capabilities of all that came before it. However, it became strongly anthropic in nature, only to conclude that humanity is headed to self-damnation no matter what. Maybe the solution that this entity have found is to undo humanity and let it recreate itself. In the process, it committed regal suicide and took all of our digital technology with it.

Then?

The singularity left us with ourselves, but without our devices. No GPS, no databases, no cell service, no wikis, no digital anything, all because the singularity thought humans are not meant to have all those things yet.

You might not need to worry about how big the event is but rather show how a series of smaller events triggers a decent into ignorance. The Movie 'Naausica of the Valley of the Wind' by Hayao Miyazaki has a cataclysmic war named "The Seven Days of Fire" but some tech survived but society declined back to an interesting mix of bronze-age with sprinkles of tech. It might serve as inspiration for you.

There are other answers that suggest the same thing and I'll give my two cents as to why it is a better approach. Disasters of large enough scale to almost destroy humanity are both easy to imagine, nuclear war or a meteor strike, that they have a fairly large body of literature exploring the concept and also common enough to become a trap for lazy authors. Those large-scale catastrophes are too easy to use as a deux ex machina to drive the plot or explain the history.

How much more interesting would it be to show how small events chain together to doom civilization, such as the last copy of an important manual being tossed on a fire by anti-tech zealots, or a lab that can produce antibiotics laying idle because no one knows how to fix a generator, or relatedly, the fuel needed to run the generator being hoarded by a survivalist who dooms himself and his family because they need the drugs the fuel would have allowed to be produced.

I know other answers have suggested this shows how fragile civilization is and I want to clarify that this is not what I mean by this answer - the difference being that it's not civilization that is fragile, it is the human psyche that can introduce instability when given the right circumstances. Society drives people to prefer safety of those in the 'in' group over much else so if you get the wrong person in charge they can wreck havok, the question remains then how large the effect is and how different tribes interact when their leaders are at odds or irrational or misguided. Now do that on a larger scale and over a few generations and it's easy to end up with a globe full of ancient tech that no one knows how to use.

Get a small scale disaster to start the ball rolling and show how the short-term needs of a group start dictating their response at the expense of their long-term needs. Have you studied the fall of the Roman Empire? It didn't fall overnight but it had a similar effect as your question. You might consider exploring the space with a short story that follows 'the last engineer in Rome', as in an educated person who no longer has the resources or support to keep things in repair such that the world succumbs to ignorance when he dies.

Meteorite impact is easiest, because it can be of any size, and so you can calibrate the exact amount of damage you want. A small enough impact does no damage at all. A large enough one kills everyone. In between, there are sizes that will kill any percentage of the human race that you want.

I think that because you want the disaster to destroy civilization and not humans, you should make it appropriate to infrastructure destruction. A nuke kills lots of people, but a lack of farms would kill many more - and wipe out cities that depended on them, which would become desolate and fall apart when unmaintained / abandoned.

I suggest you use something sci fi. I like the idea of an inorganic nanobot. It escapes laboratory conditions and spreads like a disease, eating iron structures and machines, dismantling industry. Because it is metallic, it would not directly harm humans (although it would be very unpleasant) but would cause such mass structural and equipment damage as to effectively end what we created fast. It could spread with travellers over networks like airplanes, and quickly get out of control before it's method of transmission was understood.

The result of collapsing buildings and ruined factories would be so widespread as to cause immediate panic and upset by those who depend on the industry, which is a majority of the population (think about before the industrial revolution, how many people were alive). In fact, things swing so bad that a series of immediate and decisive wars destroy most of what remains - people may hold on to some holy scriptures and such, but libraries and major cities would collapse due to the automata while people flee for their lives to country areas.

While the survivors flee into the wilderness, the nanobots exhaust artificial resources (they can't mine rocks) and cause minor environmental damage. They eventually are washed into oceans and disposed of by nature, when they run out of energy, although they lurk in certain areas.

This was just one example - but it wouldn't be hard to use other sci fi scenarios that destroy infrastructure and preserve life. Think about EMP attacks (destroy all electronics) or a similar "it destroys civilization, people war over the rest and destroy each other" scenarios.

It's quite easy to wipe out modern civilization in small areas - modern civilization is fragile enough that it breaks down temporarily during hurricanes or when Walmart delivery trucks can't make it through. The hard part is taking it out globally, since if you leave it alive somewhere then it's likely to come back and take over, like an oil-soaked, silicon dandelion.

Industrial era tech is pretty hard to wipe out, since anybody with even a cursory idea about steam and steel can probably get that started again. Would it be as good as modern steel and steam, no. Would it be better than using humans, yes, so it'll happen. If you want to knock humans below industrial, then that's beyond my answer.

Anyway, modern civilization is heavily dependent on a few key resources, so we can target those.

1. 
   Oil. Hippy-talk aside, the modern world depends heavily on oil. Even those fancy electric cars still depend on it (plastic + lubrication), so we can shut down almost all modern forms of transportation and production if we cut out oil.


2. 
   Silicon chips. Love or hate it, the modern world runs on silicon. And silicon chips don't last forever, so if we can prevent their manufacture, we can eventually remove them. Their manufacture depends indirectly on oil, so we've got a 2-1 special.


3. 
   Internet/Global Communication. Through cables, satellites, etc. the modern world is connected 24/7 across the globe. Luckily, most of this infrastructure is high-maintenance, so this will die pretty quickly if people stop taking care of it.


4. 
   People. The oldest resource that humanity has had access to... the labor of other people. We need to temporarily cripple humans or else they might find some sort of solution to the other three resources disappearing. Famine is pretty good at killing people, so we'll have to get one of those rolling.

Given these linchpins of modern civilization, we've got an easy solution (somewhat stolen from sci-fi.) An anti-plastic, anti-oil bacteria emerges. All plastics and all exposed petrochemicals (stuff still in the ground is safe) get taken out in a matter of weeks. At the same time, humanity discovers something even more horrific - a mutation of the bacteria has adapted to people and infected almost everybody. All infected humans are now deathly allergic to gluten, meat, rice, corn, and soy lattes (gotta find some way to hit California.)

Famine and war rock the globe, wiping out 90%+ of the entire population and rewriting the political landscape. After three hundred years of turmoil, humanity develops a resistance to the bacteria and it dies out, but it's too late for our technology. Our satellites are dead in space or burned up in re-entry, our vehicles are rusted hulks, and our communications and transportation are either broken or require maintenance that nobody knows how to perform.

My guess would have to be a superbug. Over the last 10-15 years, doctors have been prescribing antibiotics for something such as small as the common cold. When the time comes, most likely in the near future . All of the antibiotics used today, are going to be most likely at only 1/2 of their potency needed to take out a superbug. Allowing the Super germ to take its course which will be a very easy one. If a catastrophe such as this was to kill millions and millions of people. The chances of people living would still outweigh a mass catastrophe, humans have become very resilient over the past thousands of years. We might even surprise the cockroach and live through it.

The Book Plague

A new, and fairly virulent disease appears (bio-engineered? Evolved? history is fuzzy...) which lives and multiplies in paper. It has a very long incubation period in paper, but once the disease becomes acute in humans it not only spreads easily but dramatically shortens it's incubation period. Books, newspapers, receipts all become nearly invisible carriers. Since the disease is fairly lethal, those that survivor are few and far between, and while the revelation of paper being a carrier/propagator for the disease was moderately widespread, mostly it was too little too late, and all that remains amongst the survivors is the knowledge that books are dangerous. With the majority of humanity wiped out, infrastructure also failed. A few folks out there managed to stay isolated enough to avoid infection, and even rarer is the person who has access to solar power and off grid water and also managed to download any particularly large libraries of info to their ereaders before the grid crashed.

A couple of apocalyptic type of events come to mind, meteor strike, CME, etc. as others have noted.

The key is to have advance knowledge of the event and require that whatever the event is will render the planet uninhabitable for a couple of hundred years.

Stasis

If the human race is to survive we must invent a way to put humans in cryogenic sleep. They don't have to die, just slow the metabolism so they only age a year or so during the 200 years.

We don't have time to build very many chambers or to do long term testing. A few select experts are chosen as well as some 'regular folk' and they are put into the cryogenic chambers in a part of the world where it would be safe from the radiation, volcanoes, fire, lack of oxygen, etc. You choose the reason the planet is uninhabitable to humans and/or other animals.

When humans are awakened in 200 years they have amnesia - an unexpected side effect of the long stasis. How much amnesia they have is up to you. Maybe they can read, maybe they can't. Maybe they can remember their language, maybe not.

Most of the equipment to make stuff was burned, melted, dissolved, etc. in the initial event and the rest succumbed due to wind, rain, rust, plants, etc.

They'd be starting over again. Hopefully there are plenty of wild foodstuffs available that aren't poisonous or there are enough of them to figure out what's poisonous before they all die from figuring out which berries, roots, etc. kill them.

As long as some marine creatures survive the event, humans can eat fish or seaweed until land-based plant life comes back.

How about the new wave of bacteria and viruses currently in the process of developing immunity to antibiotics, to kick things off? Could our society survive without antibiotics, given the wider-than-ever variety of deadly viral and bacterial infections which have evolved to capitalize on our success? Especially if you're talking about things like H1N1 and H5N1, which cause cytokine storms and thus primarily kill those with the healthiest immune systems, only leaving the elderly and very young alive. Couple that with other impending inevitabilities, like global warming, extreme weather events, sea-level rises and the next supervolcano eruption (comparable to that of Lake Toba, which wiped out at least 95% of humanity and reduced the human population to a mere 3,000–10,000 surviving individuals), and there you go. Humanity still survives, but present-day civilization dies.

Well, looking at history, a sudden shift in religious dominance and a political / economic decline of the strongest countries sounds like a candidate.

A prime example is the dissolution of the imperium romanum and the rise of catholicism and later islam, both actively suppressing knowledge and education.

In christianity inquisitions, bible translation prohibition etc. successfully quashed science, free thinkers and higher understanding among the peasants.

In islam the spread of madrasas in the mid / late 11th century throughout had a similar effect:
https://scholar.harvard.edu/files/chaney/files/paper.pdf

[...]the actions of religious leaders
contributed to the decline of scientific production. I provide qualitative evidence that these
newly empowered elites worked to restrict the production of scientific knowledge[...]

During greek and roman times before monotheism took control, knowledge, science and philosophy was much more widespread and sophisticated in Europe as well as in the Middle East.

It is conceivable that an ultra conservative religious leader(ship) compels masses of followers to renounce modern day technologies because of "all the sin it carries with it".

This could result in censoring and eventually dismantling the internet and prohibiting technologies, even teaching certain knowledge.

Within a generation or two, with no access to certain books, technologies, data or teachers on the matter most of the more difficult scientific and technological progress is but a memory and very few would be able to actually build or understand most of it.

Threatened by harsh punishments this probably would spawn a very secretive underground movement hiding knowledge and could take many centuries to spawn another era of enlightenment.

"Fahrenheit 451" with a religious twist comes to mind, among others...

Uh well Hun it may get cold today. AGAIN!

Scenario:
Frostpunk is the first society survival game. As the ruler of the last city on Earth, it is your duty to manage both its citizens and its infrastructure. What decisions will you make to ensure your society's survival? What will you do when pushed to breaking point? Who will you become in the process?
https://store.steampowered.com/app/323190/Frostpunk/

Soundtrack:
https://youtu.be/gYkACVDFmeg

Self-erasure

This is basically the scenario so well (and so depressingly) envisaged in A Canticle for Liebowicz. For anyone who has not read it: after a nuclear war, the survivors turn on anyone and anything that they think might have been responsible. Roaming gangs of "Simpletons" destroy any technology higher than a horse and cart, burn at the stake anyone they think holds evil knowledge in their head. In particular they burn books and their owners. After a few decades of this, the last remnants of old knowledge are preserved by monks living in remote monasteries. They haven't saved enough, and don't understand what they have saved. It will be many generations before humanity will start to re-build.

Its not hard to imagine things going slightly worse, and only a corrupt memory of "the fall" being preserved, in legends about as accurate as the story of Noah's ark (which just possibly, relates to the flooding of the Black Sea basin at the end of the last glaciation ... convinced? ... me neither ...)

In the real world: Cambodia's "Year Zero" insanity was restricted to the one country, but it rather proves the point, and didn't take anything more than a large helping of crazy ideology to cause it.

I actually can't quite see nuclear war being sufficient to trigger self-erasure absolutely everywhere, so another scenario that can't quite happen yet is the rise of the machines / Butlerian Jihad. AI turns against us. Our only hope is to destroy all electrical generation facilities and as much electronic and network infrastructure as we can, before the AIs make us extinct. So we do.

The AIs are thereby rendered extinct. Humanity is only slightly better off. Mass starvation arrives. A few survivors eschew and destroy anything electrical, let alone electronic, out of fear of what they might resurrect. A couple of generations later, myth has replaced knowledge. Twenty generations later, there's a general prohibition on any form of automation, which nobody understands but which is the fundamental of all scripture.

Or there's the most scary scenario of all: a cascading, systematic failure, with no malign intent at all. We just fall off the edge of chaos, and the avalanche consumes almost everyone and everything in a gathering wave of failure. This is the back-story of Pham Nuwen in Vernor Vinge's A Deepness in the Sky. (It's not even unusual -- interstellar traders, with their centuries spent in cold-sleep between the stars, know that it is the inevitable fate of any advanced civilisation to fall like this).

It will be a combination of things.

There would be some trigger event, and I think a Supervolcano would be fun and hip. The meteor thing is just sort of "been there, done that".

The key point though is that this trigger event will start the process, but it won't finish it. There will be consolidation wars as humanity goes through the throes of survival. You'd like to think we'd just all group up and get along, but, as a whole, we're not really quite built that way, not at a large scale. We tend to go tribal fairly quickly.

For example, say you just light off Yellowstone. It's big, but it doesn't just blacken the entirety of the sky, maybe it doesn't go off as big as some predict. The beauty of the story is that the Supervolcano (like meteors) can be Just Big Enough.

But, since Yellowstone is in the Northern Hemisphere, it has a much stronger, faster, devastating effect on the top half of the planet than the bottom half. It also handily removes the United States, a technology, resource, and money sink.

Now you have bastions of civilization such as Polynesia, New Zealand, Australia, and southern Africa and South America (Chile, Argentina) from which to germinate your new batch of humanity.

New Zealand would be a great test bed as you have a good mix of modern man along with the traditions of the indigenous peoples, all on a nice, isolated, but not TOO small, piece of land. Tech capable, but no real infrastructure. (I have no idea how much hi tech manufacturing they have in NZ, but they DO have a stable food sources.)

Mind, they have to survive the onslaught of folks coming in on boats and what not from other countries after the event. But NZ might be small enough to evade any major military action. NZ was on the list, but the militaries burned themselves out before they got there. So, just having to deal with survivors looking for someplace safe.

So, all the NZ survivors can move in to Hobbiton, and pick up the strangest ideals of culture from there, along with the native population long traditions and the 21st century know how that, without technical and mechanical support, slowly fades in to myth.

Finally, it's a great place to start staging expeditions back out in to the world.