Depends on what you exactly mean with disable.
https://docs.godotengine.org/en/3.1/classes/class_rigidbody.html#class-rigidbody
You could set sleeping to true. It should then stop moving unless it is hit by something.
You could set the mode to MODE_STATIC then it stays where it is and ignores all forces but other things can still collide with it.
You could set collision_mask and collision_layer to 0 or (alternatively) disable all collision shapes of the rigidbody. Then no collision would take place.
And naturally you can toggle the visibility. It might also be convenient to link actions which I named above to a visibility notification. All depending on what you exactly want...