Would it be possible to show and hide the backpack button with a single word? I would like to be able to show and hide it at the same time with a menu. I would be grateful if you could add the option or tell me what I need to change.

Players can use the command "backpackui Toggle" or "backpackui Off". You can add alternative aliase to the "backpackui" command in the config. You can make the player run that command via a UI button as that is exactly what UI buttons do (run commands from client perspective).