Well, found the official workaround from Xcode beta release note:
Workaround: Make sure that you have trusted all mobile devices paired with the Mac, disconnect any devices that you don’t wish to use for development, and set “Show scroll bars” to Always in the General pane of System Preferences. https://developer.apple.com/documentation/xcode-release-notes/xcode-12-beta-release-notes
Tested and worked fine.
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Same. Suddenly started in beta 5. Now updated to beta 6 with Big Sur beta 6, still the same.