Removed the account name completely from a non-admin user account. User no longer showing up in users&groups and I can no longer log into that account

See if you can add the user back using the same short user name. It may tell you it already exists, or it may tell you the home folder exists and do you want to use that. If the latter, use the old home folder.

AppleQuestionz wrote:

Hi, I went into advanced options and removed the account name thinking I didn't need it and could just just log into the non-admin account without it.

The account has now disappeared from the Users&Groups list and disappeared when I log into the mac when I first turn the laptop on.

The non-admin user's folder is still in the 'users' folder and there is no 'deleted' in the folder name as the account wasn't deleted, I only removed the account name. I cannot access the users files as it says 'can't be opened because you don’t have permission to see its contents'. In any case, I need the non admin user to be back in users&groups so I can log in as it has some very very important files. I still have access to the sole admin account on the mac, I run MacOS Big Sur version 11.1 Thanks a lot for looking into this

Change the name of your macOS user account and home folder