Apparently the final shot is slapped together from an earlier scene
First of all, “slapped together” makes it sound like doing so would be lazy and/or that the final effect is unconvincing, which is silly, and second, it wasn’t: https://comicbook.com/starwars/2019/12/31/star-wars-the-rise-of-skywalker-final-shot-rey-desert-tatooine-pasaana/