I have an internal 3840x2160 monitor, and an external 2560x1440 monitor.
I recently installed Manjaro with KDE 5.9. I have tried using
scale 2x2. It seems ok but is laggy.
I don't really need to use both screens. When I use Ubuntu with Unity, I can set different scale factor separately. When I use internal monitor only, it can be 200% scaled, when I plug in external monitor, the internal one black out, the external monitor lighted and is not scaled.
But in KDE, it cannot remember scale settings for two scenarios, for now I should login first, change scale settings, logout and back again. How can I get it working? Or take a step back, can I setup two custom login session config files to choose when logging in? What environment variables should I export or do something else?
I have noticed
QT_SCREEN_SCALE_FACTORS and some other variables, but I have no idea how to manipulate with them.