Same issue here. I have Max and I Did the reset of all kind and even changed the hardware IC, and the SIM with no success. The Disconnect happens indoor mostly when the 4g single is weak and phone is trying to switch to 3g, it fails and then the network dump the phone out of the grid for some unknown glitch in the phone settings that occur during the switch process. What a shame apple for failing such a basic phone function. We need a fix asap.

I had the same issue of signal dropping and had it resolved. Thanks to one of the replies in this post that shared the solution. simply the IOS 14 will conflict with any VPN settings or VPN apps. Delete any VPN app you have and also Go to VPN settings and delete any settings there even if the VPN app was deleted.

SOLUTION: I had the same issue of signal dropping at home and had it resolved after many failed trials of soft and network reset, hardware check even IC change and SIM change. Finally I found the issue was my home Wifi weak security encryption that my phone connect to. Because of that weak security, The network kicks the phone out the grid to protect itself of that risky wifi. I noticed that the phone 4g signal drop after I open the wifi so I checked the wifi at home and found one wifi password security code was not the recommended WP2 with AES encryption and it was flagged as a weak security in the wifi info page. I changed it ti WP2 and encryption to AES and deleted all other WiFs that I don't use. I then did reset for network settings in the phone and restarted it. It worked and signal now is ok. I hope that would be helpful to you guys. It was very frustrating fir two weeks and an sure many are having the same .

Solution after many checks and trials of all kind for a month the issue was finally resolved by the restoration of ios 14.0.1 in DFU mode using Itunes. Recovery mode won’t work. It has to be DFU; Device Firmware Update mode which is the deepest firmware update mode that bypass Iboot unlike recovery mode that use iboot. That’s the only solution that worked. Google or youtube how to force your device to DFU while connecting to itunes. Its simple with additional clicks and you are set.