Same problem. I have a iPhone 7 . Cannot receive cellular coverage after installing ios 14.0.1 Apple Store told me that it was a component problem on motherboard and they had a replacement scheme. However since my phone is 4 years old it was no longer eligible. Basically that is it , tough luck, get another phone they are saying. I realize after seeing this discussion that its more likely to be a ios 14.0.1 problem. Of course Apple store staff know this but cannot admit . is Apple purposely driving its customers to Android models ?

Problem fixed ! im using IPhone 7 and just installed iOS 14.1.0 using iTunes . Took an hour and several tries ( WiFi upload not work ) now have cellular- let’s see how long . lesson learnt- dont install new iOS until maybe a month after released . At least Apple listened and acted .

i was wrong :( updated to iOS 14.1.0 - worked for 3 hours . way to go Apple- keep up the great work you are doing - NOT

My cellular connection has now been working for 24 hours . I have a iPhone 7 and iOS 14.1 all I did was remove my SIM card for 2 days . Then I put it back in . i had been operating in airplane mode for those days to stop the phone searching for cellular. interestingly within a min I got a spam call from Bangladesh. Not confident this is the solution but working so far .