I recompiled my turn-based app to the (now mandatory) SDK 26 (Xcode 26.4 to be exact), and Game Center is no longer sending notifications of turn changes or game invites to either my iPad Air running 15.8.8 or my iPhone SE3 running 26.4.2.
Game Center Notifications Stopped Working
So I forgot my own advice from a post in December - use TestFlight or Game Center notifications don't work.