[kde] [Bug 509817] New: Flatpak-installed GTK3 apps ignore Breeze theme and use Adwaita

[Luka Rasputin]

https://bugs.kde.org/show_bug.cgi?id=509817

            Bug ID: 509817
           Summary: Flatpak-installed GTK3 apps ignore Breeze theme and
                    use Adwaita
    Classification: I don't know
           Product: kde
      Version First unspecified
       Reported In:
          Platform: Arch Linux
                OS: Linux
            Status: REPORTED
          Severity: minor
          Priority: NOR
         Component: general
          Assignee: unassigned-bugs at kde.org
          Reporter: nanoblade9 at gmail.com
  Target Milestone: ---

SUMMARY
When I install a GTK3 application via Flatpak (for example, Lutris or GNOME
Boxes), the application ignores the GTK3 theme configured in KDE System
Settings (Breeze by default) and instead uses Adwaita.

This issue only happens under KDE Plasma. The same Flatpak apps respect the
configured GTK3 theme when running under other desktop environments such as
GNOME and Xfce.


STEPS TO REPRODUCE
1. Open KDE Plasma desktop (default settings, Breeze theme selected).
2. Install a GTK3 app via Flatpak, e.g.: flatpak install flathub
net.lutris.Lutris
3. Launch the application.
4. Observe the application’s theme.

OBSERVED RESULT
The application uses Adwaita theme instead of Breeze.

EXPECTED RESULT
The application should respect the GTK3 theme configured in KDE System Settings
(Breeze).

SOFTWARE/OS VERSIONS
KDE Plasma Version: 6.4.5
KDE Frameworks Version: 6.18.0
Qt Version: 6.9.2

ADDITIONAL INFORMATION
I’m aware that Flatpak uses sandboxing, which affects how theming works.
However, I noticed that the Breeze theme is installed as a Flatpak dependency,
yet GTK3 apps still don't use it.

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