SUMMARY
since the update to fedora 42 (kde plasma edition) flatpak apps no longer respect the system gtk-theme and the system fonts, that are chosen with the plasma system settings

it worked under fedora 41.


STEPS TO REPRODUCE
1. open a flatpak app that uses gtk (like libreoffice or firefox or thunderbird)


OBSERVED RESULT
default theme and fonts are applied.


EXPECTED RESULT
the theme, that has been selected under "kde system settings -> colors & themes -> application style -> configure gnome/gtk application style" should be applied.
also, the fonts, that have been selected under "kde system settings -> texts & fonts -> fonts" shpuld be applied.


SOFTWARE/OS VERSIONS
Operating System: Fedora Linux 42
KDE Plasma Version: 6.3.4
KDE Frameworks Version: 6.13.0
Qt Version: 6.8.2
Kernel Version: 6.14.2-300.fc42.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 2700X Eight-Core Processor
Memory: 31,3 GiB of RAM
Graphics Processor: AMD Radeon R9 380 Series


e.g. flatpak permissions of libreoffice:
[Context]
shared=network;ipc;
sockets=wayland;pulseaudio;cups;
devices=dri;all;
filesystems=xdg-config/gtk-3.0;home;xdg-run/gvfsd;xdg-config/fontconfig:ro;host;

[Session Bus Policy]
com.canonical.AppMenu.Registrar=talk
org.gtk.vfs.*=talk
org.libreoffice.LibreOfficeIpc0=own

[Environment]
GIO_EXTRA_MODULES=/app/lib/gio/modules
JAVA_HOME=/app/jre
LIBO_FLATPAK=1


flatpak version:
Flatpak 1.16.0