[UE4-27] how to have UE simulator switch between full-screen and minimized mode?

I use UE4-27 to develop a simulator which is controlled by a Qt application. I wish to freely switch the UI between the UE simulator and Qt application. i.e. when Qt is minimized, the UE simulator switch to full-screen; when UE simulator is minimized, the Qt to take over the screen.
the platform is Ubuntu 18.04. Is there any way to have UE simulator restore to full-screen mode?
Best regards