I recently saw again the movie(based on a book) The Shoes of the Fisherman. Anthony Quinn plays a Russian priest, Roman rite, who becomes Pope Kiril.
I once read another book titled The Vicar of Christ, in which and American becomes pope as Francis I.
I also saw another film,can’t remember the title, in which the new pope gets accidentally locked out of the Vatican grounds and decides to not return immediately, instead kind of taking a walking tour of Italy. He does come back though.
What other fiction have you seen that has a pope invented for the story? There must have been more than these.