I just looked at the ending after searching for a director’s cut and it seems to me that that’s exactly the way Hitchcock wanted it to end. Whether he left some footage on the cutting room floor or not, I can’t tell.

You don’t like the phallic final scene, @luigirovatti…?

I have a good friend who has wide knowledge of films. I asked him this. He looked it up in a book and on 2 reputable websites and said no. He further added he has never heard of alternative cuts of any Hitchcock film.

Hitchcock was one of the few directors the studios didn’t mess with. I believe NxNW exists as he wanted.
Also, sonsider the cut between the scene on Mount Rushmore and the train. It moves smoothly between Cary Grant lifting Eva Marie Saint up the rock to his lifting her into the berth.

Clearly an intentional cut. I don’t know what remains to be solved other then how they got off the mountain which would be anticlimactic.