Apple macOS users have reported an annoying Big Sur bug that would occur regularly on their devices. According to the complaints, the system’s Fast User Switching screensaver feature would pop up without warning, disrupting whatever the user is doing.
While this issue has recently made headlines online, its existence have been recorded as early as late 2020 on Apple support forums and Reddit. In addition, even though its believed that the screensaver bug mainly occurs on M1-based devices, users have reported encountering the issue on Intel-based Mac machines as well. Notably, the bug is reported to affect devices running on the 11.1 version of the macOS with multiple user accounts present.
The Fast User Switching feature allows users to quickly switch between different accounts saved on their devices without having to log out. When activated, a screensaver will appear while the switching process is running in the background. The bug causes the screensaver to appear randomly even without the user activating the feature, and cannot be removed by regular means.
As pointed out by several users, the screensaver can be removed by closing and reopening the lid on their MacBook devices, a light press on the Power/Touch ID key, or using the Alt-Command-Q key shortcut to get back to the login screen. Keep in mind that these are merely short term solutions for a problem that would still happen randomly.
A more long term solution that was suggested is to disable the Fast User Switching feature altogether. However, this would also mean that users will have to stick with one general account when using a shared Mac device.
Currently, Apple has yet to fully address this issue, but a fix may be finally making its way to users soon. As pointed out by users from MacRumors forum, the bug is no longer appearing in the 11.2 beta version of Big Sur, indicating that the issue may have been resolved. No word on when the new 11.2 update is planned to be rolled out publicly at this time.