You can setup a User as “user”
openhab> openhab:users add udo mypassword user
udo (user)
User created.
openhab> openhab:users list
openhab (administrator)
udo (user)
openhab> openhab:users remove udo
User removed.
openhab>
A user with role “user” will not see the settings and won’t have access to administration, so it’s already useful, even if not possible to create multiple users via UI.