Even Newsom isn’t that stupid.
The Duchess of Sussex does not legally have a title because she is not a Peeress in her own right. Her titles of Dutchess, Countess, and Baroness are derived from her marriage to a Duke, Earl, and Baron, peerages her husband was granted via Letters Patent issued by the late Queen. Her titles are courtesy titles only with no legal substance.
She is legally entitled to the Style “Her Royal Highness” as the wife of a UK Prince, under Letters Patent issued by King George V. However the late Queen efffectively barred their use, and styles have no legal standing in the United States anyway.
They were going to market a line of goods under the brand “Royal Sussex.” Queen Elizabeth put a top to that quickly.