I have a 2019 iMac, and I'm planning to nuke and return to Ventura. But before I do that I loaded up the public beta, 15.1, and Apple has fixed the Messages issue. It finally works as one expects with ExpressVPN active. I do not know about FaceTime since I do not use it. But the People part of Find My is still not working, although the Devices part is working fine, as it did on 15.0
So it seems Apple is getting there.