Hi, I've been experiencing a similar problem. I updated to ios 14.0.1 about 2 days ago and immediately faced the issue. I tried to switch my sim to my friend's (he has a different network) and his sim works. My sim only works if I change my cellular option to 3g from 4g but if I restart the device or turn airplane mode on/off, then I face the same problem. I tried ios 14.2 beta, and even that hasn't solved the issue.

So I just installed iOS 14.2 Beta 3 on iPhone XS and it didn't solve my cellular signal issue. Haven't tried the DFU method as of yet as it only seemed to solve it for 1 person as yet. Guess I'll have to wait for the standard update.

iOS 14.1 is out. Has anyone tried installing that and if yes then does that fix the problem?

iOS 14.1 update didn't work for me either. Has anyone tried 14.2 beta 4 update because I heard there is a modem update in that and may fix different connectivity issues?

Just and update, iOS 14.2 beta 4 includes a modem update and I thought that may solve this issue. I installed the update on iPhone XS 2 days ago and everything was working fine. I was able to make and attend calls, messages and used 4g data as well. Then I charged my phone overnight and for some reason the issue started happening again. Tried restarting the device and everything else but to no avail. One thing is for sure, the problem is related to iOS 14.