funny to read this article now. I struggled for months with this issue on Proximus(Belgium), but at other providers it worked fluently. Indeed, it should pop-up immediatly.
Proximus pushed the last Modem software version to my modem and it was fixed. Note: factory reset is NOT the same, I did this 1000 of times.... Check with the modem's provider and ask for the latest version or a newer modem. Could be your hardware is already outdated
What maybe happening is that if you have even the slimmest network connection your phone will choose that and will flit to Wi-Fi calling if it completely fails.
Maybe turn on flight mode to force only Wi-Fi calling !
Daily Driver > Samsung Galaxy s²³ Ultra 512Gb in Phantom Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help. " This is the way. "