Since the end of October, a few hundred users have taken yo Apple’s forums to report that their iPhone 12 (with reports seemingly covering all fourmodels) drops the cellular connection on 5G and 4G networks. This seems to be happening more often with Verizon and AT&T users but T-Mobile clients experience the issue too.
A separate Reddit thread has been created just for this and owners of iPhone 12 say that this happens mostly while they are traveling by car. The workaround, for now, is to turn on the airplane mode on and off again. One of the commenters said that he was able to reach one of the PR execs and he confirmed that Apple is aware of the issue and is currently investigating. Perhaps a fix is on its way.