Why do some Flatpak software recognize system settings, while others do not?
Recently, I upgraded my PC to Debian 12 and chose KDE as my Desktop Environment. For this fresh installation, I decided to maintain only the core packages managed by "apt" and started using Flatpak for my apps.
Some Flatpak apps perform flawlessly out of the box, such as LibreOffice and QGIS. They adjust the language to my localization and adopt the theming from my system effortlessly. However, others like Obsidian and Zotero require manual adjustment of settings by modifying the configuration files.
I understand that Flatpak applications are sandboxed, so I initially expected them not to recognize my system configuration files. However, I am puzzled as to why some apps do recognize them while others don't. I have attempted to read some documentation on Flatpak itself, and if I understand correctly, Flatpak has the capability to read from system configuration files. However, I haven't fully grasped how it accomplishes this (is there anything to do with portals?) and why it only applies to certain packages.
Only after you pointed out the discrepancy between GTK and QT applications did I realize that the apps that worked flawlessly out of the box were QT-based. Thank you very much for the clarification!
I've also started using Flatseal to look into the usages and permissions of each individual app. I must say that I still don't understand how my GTK applications have permission to access my home folder (where my GTK configuration is located within my ".config" folder) but still don't apply my GTK config as their default.
For now, I have to manually copy my "gtk-3.0" folder from my .config directory into the individual config folder of each application installed in ".var". It's not as laborious as it sounds, but I hope that in the future, when Flatpak becomes more widely adopted and integrated within Desktop Environments, efforts like this become unnecessary.
All GTK applications, yes, while all Qt applications have adapted to my system theme and language.
The default theme of Firefox is set to automatically adapt to the system theme, and I don't think it only refers to the GTK theme, as this default is also included in Windows. Maybe it could be that? Or perhaps the GTK-based applications I'm using are less developed because they are relatively niche and not configured to use the system settings (at this point, I'm just speculating as I'm unsure how this even work).
If any lost soul stumble upon this post when searching how to fix the integration between kde-plasma and flatpak when it concerns to the gtk theme, it just is necessary do download the flatpak application "org.gtk.Gtk3theme.Breeze" and run the following override: flatpak override --user --filesystem=xdg-config/gtk-3.0:ro". It seems that package enables the colorscheme of Plasma to be transferred to flatpak applications.