Huge UI under HiDPI KDE

[laech]

I'm running Kubuntu 22.04, with KDE 5.24.6, under X11, with display scaling set to 225% in KDE, when starting Zoom (5.9.6.2225), it gives me a huge UI.

The log does output the correct DPI and scale (well 2.25 is the correct value, but 2.5 is close enough) for my setup:

$ cat ~/snap/zoom-client/current/.zoom/logs/zoom-terminal.log
Cursor: DMZ-Black
216 dpi, using scale factor: 2.5

One workaround I found is to start on the command line unsetting QT_SCREEN_SCALE_FACTORS first:

$ QT_SCREEN_SCALE_FACTORS= snap run zoom-client

This starts Zoom with the correct scaling. This is the value set by KDE before the unset: QT_SCREEN_SCALE_FACTORS=eDP-1=2.25;DP-1-0=2.25;DP-1-1=2.25;HDMI-1-0=2.25;

One a different machine with similar setup but with 150% scaling, I experience the same issue, and the same workaround works for that as well.