I'm building the new Widget for my application, it works normally in development (simulator and real devices).
However, when I install a beta from TestFlight the widgets are dark-blank. But it works for some devices (iOS 14.2).
(Reboot the phone make Widget works again, but got down after awhile again)
The two issues "Dead Code Stripping", and disable "Bitcode" were solved by Apple and mentioned in Xcode 12 release note.
But I'm not sure if Xcode 12.x has the issue again, or just an iOS version bug?
There was a similar issue posted here: https://developer.apple.com/forums/thread/655393