Rule: - Scale UP with GDK_SCALE - Scale DOWN with xrandr
my .xinitrc has:
xrandr --output DP1 --mode 3840x2160 --fbmm 600x335 --scale 1.25x1.25 --output HDMI2 --off
export GDK_SCALE=2
export QT_AUTO_SCREEN_SCALE_FACTOR=1
Pycharm:
In pycharm since version 2019.2/JBR11 you'll need to add this custom VM option
-Dsun.java2d.uiScale=2
For older versions for me it was enough to set:
GDK_SCALE=2
as an environment variable