I now downloaded and tried the OpenSUSE Leap KDE live isos (versions 15.0 - 15.5). tl;dr: None worked 15.0 Gave me nothing at all, screens stayed in powersave. 15.1 - 15.5 all displayed the framebuffer and loading screen in 4:3, after full boot (once I assume the X server started) the screens blanked again. As the system is locked (maybe accessible via ssh) when I boot with my main screen attached, I did not extract any kernel logs. If you need any, tell me.