[SOLVED]. This is what worked for me. I have IOS 14.2 beta and Xcode 12.2 beta, so the versions are supposed to match but I still had the problem. I unpaired the iPhone (from Window - Devices and Simulators), restarted Xcode. This did not resolve the problem. Then I went back to Window - Devices and Simulators, and then checked "Connect via network", disconnected lightning cable and built the app. That worked. So the solution for me was to build to iPhone via network and not using USB connection.