Unable to log in to MacBook Pro account due to 'unknown error'

Darij wrote:

What can I do if I have a device problem, but the account is not damaged? The MacBook does not allow me to log in to the account and displays an "unknown error".

Because of this, the MacBook doesn't allow me to do anything. The apps are still there, but any files won't open, folders won't be created, and nothing will be saved.

[Re-Titled by Moderator]

Original Title: There's a problem with my device when I try to log in to my account.

You are logged in or not logged in?

> do you see your account in the drop down...

old issue, new issue, what changed?

—A SafeBoot Start up your Mac in safe mode - Apple Support will sort many anomalies

Reboot as normal and test.