my iPhone X experienced same problem in loosing all cellular signal after upgrade to ios14.0.1. I went to the Apple shop but after checking, they said it was my iPhoneX’s chipset problem and refuse to repair it.... until and unless Apple could realises it is their fault...! I couldn’t do anything but just to accept it and thinking may be it was an unfortunate event to myself... UNTIL I found this thread on Google....! More than 100 reported cases on same problem. 😡😡😡 Could Apple resolve this problem ASAP rather than blaming their faults to their user...!