bdelveaux Said:
"AppleTV too dark on MacBook Pro: [...]Something is wrong with the adjustment for the internal screen that makes Apple TV (and others) display too dark. Not sure how to fix this..."
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Troubleshooting Dark Apple TV App:
A. Go here: Adjust Apple TV App Settings - Apple Support
B. Try Safe Mode:
While in Safe Mode, try entering the passwords. In Safe Mode, login items do not run, and corrupt system files(i.e. caches) are intentionally reset as a way to fix issues.
- Boot: in to Safe Mode: [Hold Down: shift key upon boot].
- Log in: as same user
- Try: this once more
- Restart the Mac Normally
- Try: this once more
C. Single-Out this User:
Try an Admin new user, see if you can add the eMail account t to it. If so, then it is an issue with the conjuration of the current user. If not, then it is an issue with the entire Mac.
D. Reinstall the macOS:
Nothing would be deleted. It's just that items that have become corrupted or deleted, would be replaced or reinstalled back to where they should be. Go Here: How to reinstall macOS from macOS Recovery - Apple Support. Important: (applies if you can log in) Be certain to create a backup of your Mac prior to all of this. That way, you can have something to restore from the Mac from, should anything go wrong with the reinstall. Once reinstalled, try this once more, seeing if you still get this error.