If you install a new application in a Qubes virtual machine but it isn’t added to the menu, you can run the following command to add it and all the other apps you installed:
qvm-sync-appmenus name_of_vm_apps_are_in
Ensure that you run this command in the ‘dom0‘ VM by entering the start menu and clicking ‘Terminal Emulator’ out front (not the terminals within other Qubes). To confirm that you have entered the correct VM, check if the terminal shows
[username@dom0 ~ ]$