I've activated 2 lines on Mint, both of them on Moto G5 Plus (not that it matters). WiFi calling is enabled on both lines. After the port, it took about 24 hours, but almost everything seems to be working.
The main issue is that when I call my wife or she calls me, it rings twice and then says Call Ended. We're both using Mint. It doesn't send us to voicemail like you would expect, and with only 2 rings it doesn't give us much time to answer.