Could ApplicationManagerWindow be same type in every use case?

User reported that there could be issues with ApplicationManagerWindow being different type on different OS's:
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On Mac, it is an Item because it doesn't support multiple processes. On Ubuntu, it is an ApplicationWindow.

This causes problems when, for example, setting the font at the root - which you can't do because the font property isn't there - or is it?

I already knew this nasty two-minded approach but today I hit it hard when I realised 
(the subtle yet obvious point that SytemUI's ApplicationWindow doesn't cascade 
it's font to ApplicationWindow being composited by it (in a multiprocess mode)

The main problem is that the whole premise of ApplicationManagerWindow 
is that it is loaded from QML source files at run time, so you can 
"get away with it" but that argument is no longer acceptable in today's Qt6 qmlsc era.

The reason no-one has "found it" is that no-one has considered the possibility of 
ApplicationManagerWindow instances being passed through the qmlsc.

For example, does it have a color property… or not? Is it a QQuickWindow… or QQuickItem? It makes a difference to many bindings.

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