RegEx Split / ? input string(s) did not match the pattern or contained more groups than expected

I have a simple regex (\d+) and a string column either containing only a number or some text with a number in it.

The regex works for those cells that only contain a number. But give the “7 input string(s) did not match the pattern or contained more groups than expected” error for all ones that contain text before and after the number.

But I really don’t understand why I get this error.