Created attachment 860551 [details]
Only fails on 3.11, works on 3.10.
I experience this on 3.10 as well. Fresh install of PyQt5 et al.
Created attachment 860554 [details]
Build log for PyQt5-5-15.7 and python 3.10
More specifically it seems to have broken with new stabilized sip-6.7.7, it works with dev-python/sip-6.7.5
PyQt5-5.15.9 is fine with the new, fwiw there's stablereq bug #904783 (not that I really tested it, I only use PyQt6 nowadays).
Works with 3.10, fails with 3.11
PyQt5-5.15.9 been stable for a while so I think this is obsolete.