There is a problem with the clone theory, admittedly, as we haven’t seen clones in the current canon who are force sensitive. There were cases of that in the Legends continuity, though, so it’s possible that element could be re-introduced much like other bits of past canon that have been retconned. Rey being one of many force-sensitive clones would be a great callback to the old Star Wars novels, in which Emperor Palpatine had clones of himself.
Article source: https://www.cinemablend.com/news/2478682/lets-talk-about-reys-shocking-star-wars-the-rise-of-skywalker-twist