A growing number of M1 Mac users are reporting a Fast User Switching bug that spontaneously activates the screensaver and leaves the user unable to dismiss it.
macOS Big Sur’s Fast User Switching feature allows users to quickly switch between user accounts without completely logging out. However, user posts in the MacRumors forums, Apple Community forums, and on Reddit, say a screensaver can sometimes fire up, taking over the screen of the Apple Silicon-powered Mac, rendering the Mac workspace completely unavailable.
When the screensaver kicks in, the mouse pointer is still visible and can be moved. However, nothing else works, requiring users to close and re-open the lid on their MacBook Air or MacBook Pro, or light press the Power/Touch ID key or use the Alt-Command-Q key combination to get back to the login page.
Apple Community forums member Squeaks2369:
I am experiencing the same issue. M1 MacBook Air. Big Sur 11.0.1. Happens on two separate user accounts, both with the screensaver disabled. No way to exit the screensaver but to close then open the lid. Happens a few times a day while actively using the computer. Browsing various forums it appears others are having this issue as well.
While disabling Fast User Switching prevents the issue from occurring, it obviously disables the useful feature. Disabling the screen saver in System Preferences doesn’t prevent the screensaver from taking over.
Users report the issue with M1 MacBook Air, M1 13-inch MacBook Pro, and M1 Mac mini models, on all versions of macOS Big Sur. Users are advised to submit feedback to Apple if they experience the issue.