It seems some users are complaining about another small bug or problem on their M1-based Macs (MacBook Air, 13-inch MacBook Pro and Mac mini) with the new macOS Big Sur operating system installed and the fast user switch option. This "Quick User Switch" option is disabled by default in macOS Big Sur, but it seems that some users who would have activated it on their Macs with M1 processors would be having blocking problems with a screen saver that appears and cannot be removed.
It is best to see the video of an affected user to see exactly what the problem is:
It seems like disabling the fast user switch option avoids the problem, but of course, this means that this function is no longer available and it is not a solution to use. Some of these affected users have tried to disable the screen saver from System Preferences for all users but it also doesn't seem to be a solution as the problem still exists.
The important thing here is that Apple fixes this problem of "blocking" the computer that seems to also It is solved by closing the lid of the Mac and reopening. It is undoubtedly a software failure that may be corrected in future versions of the system and although it does not affect the majority of Big Sur users, it is best to fix it as soon as possible. In MacRumors It seems that there are several users affected. Does it happen to you?