Quick3D fails with software render backend

The hellocube example wont start under Windows unless #include <QQuickWindow> and QQuickWindow::setSceneGraphBackend("software"); are added to main.cpp (otherwise IO get "Failed to create vertex shader: Error 0x80070057: The parameter is incorrect.
Failed to build graphics pipeline state").

Using this backend makes the application start but the 3D scene is not shown (without any further information). What can I do?