[Flatpak] Application crashes on Wayland when QT_QPA_PLATFORM=xcb is set

[Uldreth]

System: Fedora 36
Desktop: Gnome 42 (gnome-shell 42.2)
Application source: Flathub
Description: If the application is attempted to run on Wayland while the QT_QPA_PLATFORM=xcb environment variable is set (eg. in /etc/environment or in ~/.conflig/environment.d/whateverfile.conf), the application will not launch. Running flatpak run net.davidotek.pupgui2 from the terminal displays the error message

qt.qpa.xcb: could not connect to display 
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vkkhrdisplay, vnc, wayland-egl, wayland, xcb.

/app/bin/net.davidotek.pupgui2: line 3:     3 Aborted                 (core dumped) python3 -m pupgui2 "$@"

Other Qt applications do not seem to be affected by this problem (tested the flatpak version of VLC, though obviously this is not conclusive).
The problem is not present either on x.org or on Wayland with the native Qt implementation.

As a temporary fix I added the QT_QPA_PLATFORM=wayland environment variable in Flatseal to the application, which allows it to run with Wayland-native Qt.

[DavidoTek]

Confirmed, caused by the fallback-x11 option. Will remove the option soon as it is not needed anyway.