Same problem here. An “x” appears on the signal strength of the 2 networks of my 2 sims after the update to Android 11 a couple of days ago. So I have no mobile data nor calls.
All settings seem fine (I haven’t changed anything and before it worked), but I will now go through all options mentioned in this thread, although I don’t see any clear solution reported yet.
Seems the same problem as reported by many other users here: