SUMMARY
When using the global menu on Wayland, Qt6 application are rendered without any menu. There is no global menu (bug 448078), but there is also no in-application menu. Any functionality that is reached through the menu is inaccessible to the user. 

Tested with qbittorrent (a Qt6 application) that gives me a global menu when started under XWayland, but no menu at all under Wayland.

STEPS TO REPRODUCE
1. On Wayland, enable the Global Menu widget, or some other widget that enables the global menu 
2. Launch QBittorrent with QT_QPA_PLATFORM=wayland
3. No menu!
4. Exit QBittorrent, launch it again with QT_QPA_PLATFORM=xcb, compare

OBSERVED RESULT
Under Wayland QBittorrent has no menu at all, global or not.  
Under XCB/CWayland QBittorrent has a global menu.

EXPECTED RESULT
The global menu should be exported correctly whatever the platform.
Barring that, as long as KDE isn't ported to Qt6, the menu should be displayed in-application.

SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20220609
KDE Plasma Version: 5.24.5
KDE Frameworks Version: 5.94.0
Qt Version: 5.15.2
Qt6 Version: 6.3.0
Kernel Version: 5.18.2-1-default (64-bit)
Graphics Platform: Wayland
Processors: 8 × Intel® Core™ i7-8550U CPU @ 1.80GHz
Memory: 15.5 GiB of RAM
Graphics Processor: Mesa Intel® UHD Graphics 620

ADDITIONAL INFORMATION
Tested with QBittorrent 4.4.3.1.