I have a laptop with a 4k screen and an external HD screen. In the Ubuntu screen settings, I can choose 100% or 200% scaling, but only overall and not per screen. With 100%, text is way too tiny on my main display, and with 200%, it is way too large on my external display. Can't this be set individually per monitor?
Also, not all programs seem to respect the scaling setting. In GIMP, for example, text is okay, but icons are microscopic on my main 4k display.