Dear Maintainer,

After upgrading to Debian 14 Forky, the Qt6 theme engine is broken and fails to load the Breeze theme. All system settings and Qt applications render using a basic fallback style (Fusion/retro window decoration and oversized icons).

Notes on the environment:
- This machine uses Nvidia drivers (as seen in the kernel taint flags for proprietary modules).
- I have tested another machine running Debian Forky (with different hardware) and the issue does NOT occur there, which suggests a regression specific to this environment or Nvidia/Qt6 interaction.
- I have already tried clearing ~/.cache, resetting kdeglobals/plasmarc, and forcing QT_QPA_PLATFORMTHEME=kde in /etc/environment, but the interface still refuses to hook into the KDE platform backend.
- When ending the desktop session (logout), the screen goes completely black with only a single dash (-) visible in the corner.