Bug 485728

SUMMARY

If using Dolphin outside Plasma6 (In my case with the AwesomeWM window manager), some applications launched via it completely ignore the system theme settings (even the systemsettings-defined fonts!) and start using the default white theme. The same applications, when started either via the menu or terminal, properly use the correct theme.

There are some variations on how this works: 
- some applications (for example ark, calibre) stay on the white theme until closed
- then, for example gwenview (please see https://pasteboard.co/9MnEYXumh8RR.png) starts with the white theme, but returns to the correct theme after being fullscreened (left: before, right: after)
- Sometimes even Qt5 applications are affected! Smplayer's configuration dialog changes according to whether it was launched via Dolphin or via menu/terminal (please see https://pasteboard.co/w1aEiwZ9tY56.png, the left image is via Dolphin)

This issue didn't exist on the earlier Qt5 version of Dolphin.

OBSERVED RESULT
KDE6/Plasma6 theme handling is b0rked

EXPECTED RESULT
All application should use the systemsettings-defined theme, regardless of how they are started, without exceptions.

SOFTWARE/OS VERSIONS
Linux: Arch Linux/X11 
KDE Plasma Version: 6.0.4
KDE Frameworks Version: 6.1.0
Qt Version: 6.7.0

ADDITIONAL INFORMATION
Theme settings:
- Kvantummanager: KvArcDark
- Qt6ct: Kvantum-dark
- Systemsettings/Colors: KvArcDark
- Systemsettings/Application Style: Qt6ct-style
- QT_QPA_PLATFORMTHEME=qt6ct
- QT_STYLE_OVERRIDE unset