QML gives inconsistent results when using High DPI configurations or custom DPI settings. We used the attached 'DesktopScaleFactor.qml' in the following examples.

On Mac OSX, QML rectangles are properly scaled when switching to Retina setting. The attached 'osx_retina.png' screenshot shows double-sized rectangles compared to 'osx_normal.png', as we expect.

On Windows, when setting the 'Custom DPI Setting' to 200%, only the window border and the menu bar are scaled properly, while the rectangles keep their original size (as shown by 'win_100_percent.png' and 'win_200_percent.png' screenshots).

For the last screenshot ('win_200_percent_unaware.png'), we modified the Qt code to not call QWindowsContext::user32dll.setProcessDPIAware() in QWindowsContextPrivate. Then the rectangles are properly scaled (directly by Windows) and the menu bar looks blurry. This behavior is closer to what we want, since the content scaling is at least correct.