got the same problem with my 11 pro max!
tried everything and still nothing has changed.
my sim card works great in my 5s.
everything was in order with ios 14 and no service error happened in ios 14.01. I’m now 100% sure that it’s related to the software issue and Apple has to so sth about it!
ios 14.2 was useless.
just hoping and praying for ios 14.3 😑