Custom QWindow add widgets

[Tuxedo]

A top level widget (without a parent) or one of the widget window types (QMainWindow, QDialog) has an associated QWindow.

Thank you for that explanation it is good to know.
After a hint from elros I solved my problem by doing this:

include <QtWidgets/QApplication>
include "mainwindow.h"
include <QWindow>
 
 int main(int argc, char *argv[])
 {
     QApplication a(argc, argv);
     MainWindow w;
     w.show();
     QWindow *window = w.windowHandle();
     window->reportContentOrientationChange(Qt::LandscapeOrientation);
     return a.exec();
 }

include <QtWidgets/QApplication>
include "mainwindow.h"
include <QWindow>
 
 int main(int argc, char *argv[])
 {
     QApplication a(argc, argv);
     MainWindow w;
     w.show();
     QWindow *window = w.windowHandle();
     window->reportContentOrientationChange(Qt::LandscapeOrientation);
     return a.exec();
 }

To copy to clipboard, switch view to plain text mode 

Is this the right way to access the associated QWindow from my MainWindow? However this is working.