A 3 years old fix is applied now? The xorg-x11-server-21.1.3-lp154.680.1.x86_64 from https://ftp.gwdg.de/pub/opensuse/repositories/X11:/XOrg/openSUSE_Leap_15.4/ already contains the fix. Switched completely to this repository for the X packages. It's now working as expected.