flatpak needs XDG_CURRENT_DESKTOP=kde for non-KDE desktops
People under GNOME had problems changing the color theme with the flatpak version. After a restart of the app, the color theme was selected in the menu but was not applied to the GUI:
https://github.com/flathub/org.kde.kdenlive/issues/53
I could work around this by always setting XDG_CURRENT_DESKTOP=kde
:
https://github.com/flathub/org.kde.kdenlive/commit/7346470982136412ede241df6459e1ce22e7e74b