We have to be able to render single items

When the puppet is Qt 5 based we render single items and do the composting on the Qt Creator side.
For Qt 6 we render the complete scene. Both approaches have advantages and disadvantages.

But there are clear use cases where single item rendering is required. Those are poorly supported with Qt 6.
The main screen of the coffee machine is a good example.
Basically, all the screens are next to each other and the root item acts as a "view" and the screens are moved using the timeline.
Another case is the flow view.

Attached is a stand-alone proof of concept.