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I would like to create a list of arbitrary length:

x1_, x2_, ...

Where each of the elements of the list has the full form:

Pattern[xi, Blank]

This answer shows how to create a list of symbols:

x1, x2, ...

but I don't know how to adapt that to obtain the above.

I intend to use this list in the definition of a function as in here.

Array[ToExpression["x" <> ToString @ # <> "_"] &, 5]

x1_, x2_, x3_, x4_, x5_

FullForm @ %

List[Pattern[x1,Blank], Pattern[x2, Blank], Pattern[x3, Blank], Pattern[x4, Blank], Pattern[x5, Blank]]

Also

Thread[Pattern[Evaluate@Array[Symbol["x" <> ToString@#] &, 5], Blank]]

x1_, x2_, x3_, x4_, x5_

and

ToExpression[Table["x" <> i <> "_", i, ToString /@ Range[5]]]

x1_, x2_, x3_, x4_, x5_

If you construct a list of strings instead, you can take advantage of the fact that ToExpression is listable, and supports a 3rd argument that post-processes the output. For example:

ToExpression[
 "x1", "x2", "x3",
 StandardForm,
 Pattern[#,Blank]&
]

x1_, x2_, x3_

Or, creating the list and converting:

ToExpression[
 Table["x" <> ToString@i, i, 5],
 StandardForm,
 Pattern[#, Blank]&
]

x1_, x2_, x3_, x4_, x5_

Nothing new but shorter:

StringTemplate["x``_"] /@ Range[10] // ToExpression

x1_, x2_, x3_, x4_, x5_, x6_, x7_, x8_, x9_, x10_

Here is an example of how to make the solution in the link work for this case:

patt = Table[
 With[
 s = Symbol["x" <> ToString[i]],
 Pattern[s, Blank]
 ], i, 10];

Range[10] /. patt :> x5, x8

5, 8

Using With here is a trick to insert the symbol into Pattern. Since Pattern has the attribute HoldFirst, it would not work to write e.g.

Pattern[Symbol["x" <> ToString[i]], Blank]

because Symbol["x" <> ToString[i]] would not be evaluated before it was passed to Pattern, i.e. Pattern would not receive a string as is required.