New Qt6 CBindings version is commited. I've added QGuiApplication_x11Display() and QGuiApplication_xcbConnection(), now our app and Qt uses same descriptor for Display, so you don't need to use private stuff from Qt. Bindings version is 6.2.3.
Note for future versions: in Qt6-6.5 there will be QNativeInterface::WaylandApplication, I'll add it to our 6.2 based bindings but via versioning in source, so if Qt6 version >= 6.5 we'll be able to use wayland struct members, so our bindings will be 6.2 compatibile and returned wayland stuff will be nil for Qt6 < 6.5.