The existing code compiles against Qt6, but it fails to link as the QDBusMenu* classes have installed (private) headers but are not exported. We either need to find a way to not use those classes anymore (which we mainly seem to be doing in code originally taken from Qt, qdbusmenubar.cpp), or get those classes exported in Qt (installed headers, even if private, without exporting could very well be a mistake there, as this used to be in a static QPA support lib).