I'm on Fedora. My use case is for the mingw-python package I maintain there, see [1] for the full details. I believe (though I haven't investigated) that the previous downstream lib64 patch behaved slightly differently, or that something else between python-3.8 and earlier and python-3.9 changed, in that I didn't have lib64 appear in the site packages path previously when invoking python as detailed in [1], whereas it now does.

[1] https://src.fedoraproject.org/rpms/python3.9/pull-request/10#comment-0