OpenBoard provides a virtual whiteboard with several pages. These pages can be moved independently, and OpenBoard saves the position of each page (more specifically, the center of the view after mapping to the relevant scene) 

In my case, the center point always comes out as QPoint(960, 505). This point is then mapped to the scene via mapToScene(center).
In Qt 6.6.1, the result is QPointF(0,0) because the page is centered there initially. Changing nothing but the Qt version, Qt 6.6.2 yields QPointF(0,-0.949555).

This effect compounds over time, resulting in an effect of "moving down". The only seemingly related info I have is that a transform representing a zoom factor of 1.05313 is applied: 

QTransform(type=TxScale, 11=1.05313 12=0 13=0 21=0 22=1.05313 23=0 31=0 32=0 33=1)

Incidentally, 1/1.05313 ≃ 0.9495504, which is close to the offset.

I wasn't able to bisect the commits between 6.6.1 and 6.6.2 to determine which one causes the change. d99b0c might be related, though I'm not sure.
If there is anything else I could try, please add a comment below.

Thanks for your time,
Vekhir

This issue has been reported in OpenBoard too: OpenBoard#1009

The relevant source code section in OpenBoard is here: https://github.com/OpenBoard-org/OpenBoard/blob/dev/src/board/UBBoardController.cpp#L1008-L1011