There is no point in responding 4NT to an opening 1NT.
We have a perfectly good enquiry bid in 2♠, without bypassing three levels of bidding.
Note that if the 2♠-responder bids again, we are now in a game-forcing situation. If the responder continues to bid over game, we're now in a slam-forcing situation.
If opener rebids 2NT over 2♠, showing a minimum hand, and responder now makes a non-game bid, opener is expected to bid naturally.