Session crashes when monitor goes into standby
The Wayland session (KDE Plasma in my case) crashes to the login manager when the screen is set to power off. The monitor will first go into standby once the mouse hasn't been moved for the given amount of minutes, but will immediately wake up afterward. When it does I can briefly see the console, followed by the login screen from which I need to log in again. This prevents being able to power off my screen and preserve its lifetime as well as electricity consumption.
I discussed this on the openSUSE forum and someone pointed me to a bug from Redhat which indicates Wayland crashes when no monitors are present. As mine is connected over a DisplayPort cable which (alongside HDMI) no longer seems to support classic standby mode, the display will become entirely disconnected; In X11 it worked but when the screen came back online, the system detected a new HDMI audio device as if it was just plugged in.
Indeed this seems to be my issue too; I enabled my secondary display (a cheap VR headset) then turned monitor standby back on. While the screens still didn't stay in standby and apparently switched order, I didn't experience a session crash this time.