If you don’t see a login window when you start your Mac
If your Mac starts up without displaying the login window, it’s set up to bypass the login window and automatically log in a particular user.
Important: Automatic login allows anyone to access your Mac simply by restarting it. If automatic login is enabled, make sure your Mac doesn’t automatically log in an administrator. When FileVault is turned on, automatic login is disabled.
If several people use a Mac, it’s best to add a separate user account for each person and turn off automatic login. Creating separate user accounts protects the information and settings of each user.
The next time you start up your Mac, the login window appears, and a username and password are required to log in.