On Wayland QMainWindow::devicePixelRatioF() reports a ratio of 2 when the real ratio is 1.25. On X11 the correct ratio is returned. This is the current state with the latest KDE/Plasma 6 DE.  As the Wayland merge request referenced in QTBUG-87321 was accepted and it still does not work properly in Qt6, I'm opening a new issue as it is not even clear who to blame. Was the change in Wayland not sufficient? Is it a KWin issue? Or is there still a problem in Qt?

Anyway, from the user perspective, QMainWindow::devicePixelRatioF() is still broken in Qt6 under Wayland and at least it should be mentioned in the Qt documentation, if that can not be fixed in Qt.