Hi all! .. I was the same problem. After reading all entries a tried to remove only the device support version with the problem:
rm -r ~/Library/Developer/Xcode/iOS\ DeviceSupport/14.1\ \(18A8395\)/
After this: I closed the Xcode 12.1
I disconnected the iPhone XR with iOS 14.1
I started the Xcode
I opened the project
I connected the iPhone
Finally a new device support was make:
~/Library/Developer/Xcode/iOS\ DeviceSupport/14.1\ \(18A8395\)\ arm64e/
Now the problem is solved!!
thx to everyone!!