In my opinion, and this is gonna be deep Star Wars legends theorising rather than canon, Snoke was almost definitely intended to be Darth Plagueis (of “the Tragedy of Darth Plagueis the Wise” fame), Palpatine’s former master. He was obsessed with Sith alchemy, cloning, biological engineering, that kind of thing, and famously could “keep the ones he cared about from dying […] but not himself”. He roughly matches the appearance of the character, with some extra scarring. He would be one of the few characters capable of producing a viable force sensitive clone (I’m ignoring X-1 and X-2, because they’re minor game characters which probably didn’t get much thought put into them) something which Vader and the Kaminoans had been working on secretly with limited success.

I think the reason that we didn’t get a Snoke=Plagueis reveal in Rise of the Skywalker (RotS) is because fans had been speculating about it from the beginning, and “defying audience expectations” was vogue in media at the time (e.g. the game of thrones final season), and extremely heavy criticism of The Last Jedi (TLJ) influenced the story team to almost completely ignore TLJ entirely, almost as if it was cursed and if they referenced any events in it, RotS would also be cursed. So they had to, essentially, cram two whole movies of storytelling into RotS, which is why the pacing of that movie is so absolutely ridiculous.

The likelihood is that we’ll never get a direct answer as to Snoke’s origins, or if we do, it’ll be in some random novel or comic. I get the feeling that Disney want to brush a lot of the sequel trilogy’s bigger mistakes under the rug, so to speak.