The macOS system must disable logon to other user's active and locked sessions.

The ability to log in to another user's active or locked session must be disabled. macOS has a privilege that can be granted to any user that will allow that user to unlock active user's sessions. Disabling the admins and/or user's ability to log into another user's active and locked session prevents unauthorized persons from viewing potentially sensitive and/or personal information. Note: Configuring this setting will disable TouchID from unlocking the screensaver.