The Unwanted Logout
macOS supports “Fast User Switching,” a feature that allows multiple people to remain logged into their separate accounts simultaneously, switching between them quickly via the menu bar. However, in certain environments (like schools or shared family computers), macOS can be configured to automatically log out a user or switch back to the login screen after a specific period of inactivity. This is designed for security and privacy, but if you step away to grab a coffee while a long video is rendering or a large file is downloading, returning to find yourself locked out and the system switched to another user is incredibly frustrating.
Disabling the Idle Timeout
To ensure your session remains active even when you step away from the computer and stop macOS from automatically switching users or logging you out, you must adjust the advanced security settings.
Click the Apple logo in the top-left corner of the screen and select System Settings (or System Preferences). In the left-hand navigation sidebar, scroll down and click on Privacy & Security. Scroll down the right-hand panel until you reach the “Others” section at the bottom. Click the Advanced… button (you may need to enter your Mac administrator password to unlock these settings). A small dialogue box will appear. Look for the checkbox labelled Log out automatically after [X] minutes of inactivity. Click this box to uncheck it entirely. Click OK. From now on, your Mac will only switch users or log out when you explicitly choose to do so from the Apple menu.