Created attachment 140369 [details]
Screenshot from flatseal application running under wayland with bad fonts and wrong theme

SUMMARY
Flatpak applications running on Wayland don't use the gtk theme neither the system fonts and look really bad. Also they seem to use the gtk filechooser instead of the kde one. It seems like the xdg-desktop-portal-kde not working at all for wayland apps. I have installed xsettingsd so applications use the correct theme/fonts/filepicker when running in X11 session or through Xwayland. Installing also xdg-desktop-portal-gtk makes the applications to use the correct theme and fonts but also the gtk filepicker instead of the kde one.

STEPS TO REPRODUCE
1. Install only xdg-desktop-portal and xdg-desktop-portal-kde (without xdg-desktop-portal-gtk)
2. Use a gtk flatpak application that uses Xwayland and verify that uses the correct theme/fonts/filechooser.
3. Use a gtk flatpak application that uses Wayland and see that uses the wrong theme/fonts as well as the gtk filechooser.

STEPS TO REPRODUCE with firefox:
1. Use firefox from flathub which uses Xwayland and verify that uses the correct theme/fonts/filechooser.
2. Run firefox with MOZ_ENABLE_WAYLAND=1 to run it as a wayland app and see that uses the wrong theme/fonts as well as the gtk filechooser.


EXPECTED RESULT
Wayland applications should use the correct theme/fonts and filechooser by only having installed xdg-desktop-portal-kde.


SOFTWARE/OS VERSIONS
xdg-desktop-portal-kde version: 5.22.4
Linux: Archlinux
KDE Plasma Version: 5.22.4
KDE Frameworks Version: 5.84.0
Qt Version: 5.15.2

ADDITIONAL INFORMATION
same result with version 5.22.3