@Futura I'm located in Norway. Not EU. We have 2G fallback for a few more months on my network, but I've confirmed it is not falling back to 2G while calling. 3G has been gone for a while already. However, I don't remeber seeing reports of FP5 users in the US yet, I have no idea if the bands in use are compatible. I would wait for more reports and look into the specific bands used.

I believe there is a couple of Xiaomi phones confirmed to work over VoLTE in the US, have a look at the thread about reports of working VoLTE devices.