"Join all monitors" option in the display switcher results in a blank desktop. This display switcher needs to be LESS accessible.
Hitting Super+P
brings up the display switcher where "Join displays" is the second option. The menu itself isn't something that's useful to the vast majority of users. At most, people might want to toggle their laptop monitor off and on while still staying connected to their external monitors. However that's not even an option there. Instead you just have a bunch of options do nothing except disrupt your workflow: mirror, join, built-in only. In particular, the join option simply bricks your session (I have a laptop with two externals), requiring a reboot. I am not sure it can work even if all your monitors are identical, which in most case they aren't.
I frequently find myself entering this monitor setup switcher by mistake. At best I get a mirrored displays, which is annoying, at worst I stumble into the deadly "join displays" option.
I recommend this switcher be removed entirely or assigned a most complex (and preferable customizable) shortcut.