Well @pyxelrigger thanks for clarifying the final scope.
Since, as already stated, folding or unfolding a scene entry doesn't generate any valuable message to be intercepted, the sole - brute force - hack you might try to implement in Python would be to implement a MessageData plugin which constantly checks for the folded/unfolded state of the entries in the scene and eventually delete the unfolded one.
This approach carries strong performances penalties to the whole Cinema 4D UI because you need to constantly traverse the scene and depending on the scene size this could strongly affect Cinema performances.
If there are no further question please mark the thread as solved.
Best, R