QWidget::restoreGeometry is not exact regarding Y offset (assumes hardcoded frameheight which may not be correct for popups)

QWidget::restoreGeometry has a hard-wired constant

const int frameHeight = 20;

that prevents a window to be restored at the top of the screen.
While this could make sense on OSX which has a menu on every screen, it has no justification on Windows.
Typical case: the user places a floating window on a second screen, at the very top. If the saveGeometry/restoreGeometry system is used, the window will be restored at y + 20.