The best solution would probably be to permanently associate a solution with a language version but I guess they didn't go woth that.

Right, the comment was meant for someone who might be confused as to where the function went :)

I can't speak for others, but if I recall correctly I submitted this solution around 2016 or 2017 when codewars was using an ancient version of elixir (something like 1.2). Obviously you would not use String.strip with 1.9 because it doesn't exist.

String.strip was deprecated in favor of String.trim, String.trim_leading, String.trim_trailing

This solution is not correct - try e.g. squareSum([2, 1, 2])