TySegurado Said:
"Thank you. Signed out and returned. iCloud is correct, but the computer is still wrong."
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Thank you for the screenshot.
Two Things...
A. Boot into Safe Mode:
In. safe mode, login items do not open at log in, and certain System Preferences are set aside.
Not Success??
B. Reinstall the MacOS:
Note that to reinstall Calendar (so it operates correctly), you have to reinstall the macOS.
If you reinstall the macOS, nothing would be deleted. All intended, original files and Apps that came on your macOS would be reinstalled (which includes Mail). It’s all about keeping your system files intact.
Important: Prior to the reinstallation, Create a Time Machine backup of your Mac, so that you can have something to restore your Mac from, should anything go wrong.