while evaluating the qt.labs.controls and support of HighDPI there's probably an error.
enabled scaling:
QGuiApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
then from
qApp->primaryScreen()
checked the sizes:
size: 411 x 683
same for virtual, geometry and virtual geometry
also DevicePixelRatio is OK: 3.5
all values for available Size, VirtualSize, Geometry, VirtualGeometry are wrong:
5040 x 8064
it seems the values were multiplied by DevicePixelRatio and not divided.
doing the same without enabling HighDpiScaling all sizes and available sizes are correct.