Palpatine's unexpected return in Star Wars: The RIse of Skywalker came courtesy of cloning, but the movie implies the Sith used this technology long before the Clone Wars. The return of Emperor Palpatine lay at the heart of marketing for Star Wars: The Rise of Skywalker, but surprisingly the movie itself avoided revealing just how the Dark Lord of the Sith had been resurrected. There were strong hints it was through cloning and genetic engineering – complete with a glimpse of cloning vats containing duplicates of Supreme Leader Snoke – but the film avoided making an explicit comment. It was widely mocked for a single throwaway line of dialogue that, "Somehow, Palpatine returned."

https://screenrant.com/star-wars-rise-skywalker-sith-clones/