HI. Your problem is likely the same as in this post Problem with visual window . If your system is running the Wayland windowing system (the default on a lot of modern Linux OS), your geometry window will be transparent due to an incompatibility between Wayland, X and Qt. The simplest solution is to login to a session which uses X11 (e.g., Plasma or Gnome on Fedora allow you to switch from X to Wayland at the login prompt). If that is not possible, you can recompile Geant4 with X11 ON and Qt OFF. When you run an application, you will then get an X11 geometry window, but the terminal display will be in a simple X terminal and there will be no GUI.