Comment # 10 on bug 1202837 from Atri Bhattacharya

Created attachment 861758 [details]
Comparison of yast (background) vs qt5 settings app (foreground) under GNOME
200% scaling + 1.25 font-size

Same issue here with a 4K display on 14".

On my system GNOME automatically sets the UI scaling to 200%; I have
additionally set font-size to be 1.25x (from GNOME Settings -> Accessibility ->
Large Text). I understand that this gives me a font DPI of 240 by Qt's
calculation (96 * 2 * 1.25). Apparently when a DPI of 240 is detected by Qt,
this causes some apps to scale up their UI by 3 times instead of 2, making
everything look over-crowded. Scale the DPI down just a bit to 239 (or just set
`QT_FONT_DPI=239`) and everything looks great. The difference in scaling
between DPI 239 and 240 is rather big, see also my report in
<https://github.com/veusz/veusz/issues/626>.

Tested both on X11 and Wayland.

What works correctly is setting the env variable
`QT_SCALE_FACTOR_ROUNDING_POLICY=PassThrough=1` and all Qt5 apps behave
correctly even at `QT_FONT_DPI=240`.