It looks like this has never worked under QT6, the implementation was inconsistent with the QT5 behaviour. Given that the QT5 behaviour works with the shipped Android app, I've tweaked the QT6 to be functionally equivalent to the QT5 implementations.
https://invent.kde.org/network/kdeconnect-kde/-/merge_requests/600#note_1018493
@diamnew if you are able to build and test this; that would be a great help.
The rationale is explained in https://planet.kde.org/friedrich-kossebau-2023-06-28-include-also-moc-files-of-headers/
In case of KDEConnect, it impressively speeds up compilation. Before it
took 390 seconds on a clean build and with this change it took 330 seconds.
This is due to the mocs_compilation having to include the header files
and thus all their headers. Due to the lots of small plugins we have,
this means that the same headers must be compiled plenty of times.
When we include the moc files directly in the C++ file, they are already
available.
