QDesktopWidget::primaryScreenChanged & QScreen::availableGeometryChanged do not get triggered consistently

I am trying to find a way to have my Qt app signaled when the user moves it from one monitor to another monitor. This is necessary to handle changes in screen sizes and dpi.
Unfortunately, the only two things that I have found that might help here do not consistently produce a signal. I have only tried Ubuntu, not Windows nor MacOSX

void
MainGUIImpl::fileOpenInterfShow()

{ ... QDesktopWidget* theDTWidget = qApp->desktop(); QGuiApplication* theGuiApp = dynamic_cast<QGuiApplication*>(qApp); connect(theDTWidget, &QDesktopWidget::primaryScreenChanged, this, &MainGUIImpl::mainGUIPrimaryScreenChanged); connect(theGuiApp->primaryScreen(), &QScreen::availableGeometryChanged, this, &MainGUIImpl::mainGUIAvailGeomChanged); ... }

// End of MainGUIImpl::fileOpenInterfShow()

void MainGUIImpl::mainGUIAvailGeomChanged(const QRect &newqrect)

{ fprintf(stderr,"AVAILABLE GUI SIZE CHANGED TO: [%d,%d,%d,%d]\n", newqrect.x(),newqrect.y(),newqrect.width(),newqrect.height()); }

void MainGUIImpl::mainGUIPrimaryScreenChanged()

{ fprintf(stderr,"MAIN GUI SCREEN CHANGED\n"); }