My hunch (without looking too deeply) is that POSIX is doing something that whichever module implements the exports policy for Perl::Critic doesn't recognize. It looks to be dynamically building its export list at compile/use time so the critic module isn't going to find an explicit @EXPORT or @EXPORT_OK package variable.

And in general, Perl::Critic is going to set you on the right path most of the time. Even the cases where you don't agree with its default suggestions or comments it's probably something that you should at least be aware of and have made a conscious decision about (then you can ## no critic it and hush it up).

Edit: Actually I can't reproduce either with same test source. Perl::Critic 1.140, POSIX 1.97, perl 5.34.0, OS X 10.15.7.