Use environment variable QT_QPA_PLATFORMTHEME=kde globally in Flatseal/Flatpak permissions

[n3thshan]

Background

When using some KDE apps such as Okular and Haruna, the accent colour/colour scheme seems to not be read out of the box by those apps unless this variable is used. The color scheme can be forced via the settings in each app but is not intuitive and tends to not work on fresh launches of said apps. The following screenshot best explains the situation.

The left is without the variable used. The right is tinted in purple as I have enabled the 'tint all windows feature' that is present in the breeze color scheme and is the indication that the color scheme is applied properly. Hope this would be considered.

System information

Operating System: Aurora 41
KDE Plasma Version: 6.2.5
KDE Frameworks Version: 6.10.0
Qt Version: 6.8.1
Kernel Version: 6.11.8-300.fc41.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 22 × Intel® Core™ Ultra 7 155H
Memory: 15.0 GiB of RAM
Graphics Processor: Mesa Intel® Arc
Manufacturer: HP
Product Name: HP Spectre x360 2-in-1 Laptop 14-eu0xxx

[inffy]

Honestly I have no idea if we can actually even set these during build or install. The flatpaks afaik are installed during the ISO install and the installer won't add any parameters to them.

But if someone has somekind of idea how to do these flatpak perms automatically, please let us know.

[ledif]

This can be accomplished with flatpak override --env=QT_QPA_PLATFORMTHEME=kde, but it is a little trickier to do when building the image.

I've actually tried baking this into my own non-Aurora image that I'm working on, but I ran into issues where the overrides are not visible on the deployed system despite setting them during the image build.

I imagine we can accomplish this by setting up a systemd oneshot service that executes the above flatpak override once on system setup, similar to how the -dx groups are set up once at initialization.