Seems to be possible with native controls (see here and here) so now I\'m looking for some Qt code to do it.
One way of doing it in Qt5 is to use QWindow::setScreen to set the screen on which the window should be shown. QWidget has a windowHandle() that returns the pointer to the QWindow.
Here is how to show your widget on second screen in full-screen mode :
QWidget * widget = new QWidget();
widget->show();
widget->windowHandle()->setScreen(qApp->screens()[1]);
widget->showFullScreen();