Blocking a sign-in
Allow sign-in: block a user without deleting anything
The Allow sign-in switch blocks a user, local or from a directory, without deleting anything.
Switched off, after a confirmation, the user’s sessions end at once and every sign-in is refused until you switch it on again. The users list has Block sign-in and Allow sign-in in each row’s menu for the same.
You cannot block the user admin, nor your own sign-in.