Created attachment 170532 [details]
Top is without problem bottom one is with problem (using GTK_USE_PORTAL here)

SUMMARY
If the system does not have installed xdg-desktop-portal-gtk but has installed xdg-desktop-portal-kde (with or without xdg-desktop-portal) the font in most gtk app is blocky and diffult to read (see screenshot).

STEPS TO REPRODUCE
1. Install a gtk app. Examples is xournalpp but most gtk app using default font (i think) should have this problem (firefox does not have this problem).
2. Make sure to have only xdg-desktop-portal-kde and not xdg-desktop-portal-gtk installed (reboot may be required after install)
3. [Alternatively] run the program with GTK_USE_PORTAL=1
3. run the installed gtk app

OBSERVED RESULT
The font is blocky and not the same as when xdg-desktop-portal-gtk is installed.

EXPECTED RESULT
The font shold be the same, or if not possible should be a less blocky and more legible font.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.1.80
KDE Frameworks Version: 6.4.0
Qt Version: 6.8.0
Kernel Version: 6.9.4-arch1-1 (64-bit)
Graphics Platform: Wayland

ADDITIONAL INFORMATION
Not sure if plasma can do anything about it or if I should report the bug somewhere else.