Very interesting interview with Ian McDiarmid it seems that Emperor Palpatine might not actually be in The Rise Of Skywalker at all as Ian states in the video above the laugh at the end of the trailer was from stock and he didnt know about it either until we did. Also he seems way to somber to be an active player in the new film when talking.
Plus check out what he says at the end of the interview about the word tease as if to say dont get our hopes up with fan theories.