I disagree. If the Duke dropped the use of his title for personal money-making ventures as proposed by the poster to whom you replied, I would expect him to use Harry Sussex. We see this with Princess Beatrice (Beatrice York) and Princess Eugenie (Eugenie York) in their professional ventures.
Under the 1960 declaration, Mountbatten-Windsor is his legal surname regardless of whether he uses it, which royal princes as a rule do not. However, the name Mountbatten-Windsor was used on the marriage registrations of his aunt and uncles (links were shared
here), and I see no reason why it should be different for him.
I would like to see the link to this, please.
I failed to discover it in the records of the House of Commons.
https://www.theroyalforums.com/foru...sh-styles-and-titles-258-263.html#post2334089