I noticed this problem the first time on a new laptop, on which I installed kubuntu 22.04. I unplugged the power cord and after 5 minutes of inactivity the screen went out. Then I found the combination FN+f4, which according to the icon should decrease the brightness, because there is a similar button next to it to increase the brightness. When I press fn+F4, the screen also goes out and also does not turn back on. Oddly enough, the same thing happens when I press the brightness UP button - screen dims black and doesen't bright up, nothing works except rebooting. I have searched many similar topics, but none of them work for me. It happens exactly when the screen brightness is turned down to 0. I can't get the screen brightness back up. Sounds play, ssh from another PC connects.
There is a similar issue without answer Brightness control turns off my monitor
