Drawing on X11 root screen

In the QApplication docs there is an hit under:
QDesktopWidget *QApplication::desktop()
On X11, it is also possible to draw on the desktop.

But QDesktopWidget is marked as deprecated. "On X11, it is also possible to draw on the desktop." can not be true anymore. I tested and I can't find a way in Qt to draw on the X11 root screen. It looks like a lot of people have the same issue, for example:

• https://stackoverflow.com/questions/42645876/qt5-drawing-on-x11-root-screen-and-changing-the-wid-of-an-existing-qwidget
• https://lists.qt-project.org/pipermail/interest/2017-March/026304.html

I also created a forum post and we came to the same conclusion:
https://forum.qt.io/topic/111914/draw-in-qdesktopwidget-desktop-background

If there is really no more way to draw to the X11 root screen, the documentation should be adapted. If there is, I would be happy to receive advice. My use-case: change X11 wallpaper/Background.