Update: Lost signal again after a week or two. Changing iOS didn't help this time. I suspect it was associated with me travelling with the phone, in and out of areas with a signal.

A couple of days after upgrading iPhone 7 to 14.4.2 I lost phone connection, continual searching for a signal. Sim was ok in an older phone (old SE also with 14.4.2!). I tried most things mentioned here: Couldn't try going to 4G since Cellular said it was in Error. Couldn't reset network settings (just froze). Couldn't restore to earlier iOS (unsigned). Deleted VPN apps, reboot, toggling airplane mode. Nothing worked. I upgraded to 14.5 beta 7 and it's back! (I immediately went to 4G just in case! And switched off auto update!) With 14.4.2 it took a couple of days before I lost the signal permanently, perhaps after driving around(?). So I might lose it again.