Note: you need Jmol 12.2.RC8 or later to use this feature (that means 12.2.0 or later when it is released).
The Jmol application can be run in "kiosk mode", useful for dedicated displays (e.g. in public places) where hiding the remaining of the computer screen, menus, windows etc. is desirable. The display will normally be driven by a prepared script, but the pop-up menu is still available by default.
While the focus is on the Jmol panel, typing
exitjmol (which is not echoed to screen) and pressing the Enter key will exit the application.