Same problem with XC12 GM.
I tried to suppress DVTSourceControlAccountDefaultsKey from defaults with no success.
Then I commented the [credentials] section in /Applications/Xcode.app/Contents/Developer/usr/share/git-core/gitconfig
restarted Xcode
and was able to access ONE repository, which recreated an entry in DVTSourceControlAccountDefaultsKey
This repository is now operational. But any other is not, even if it use the same credential. It looks like Xcode 12 has a bug in managing MULTIPLE entries in that key.
Topic:
Developer Tools & Services
SubTopic:
Xcode
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