In The Rise of Skywalker we learn of one of Darth Sidious' plans:
To have Rey strike him down as part of a Sith "ritual", allowing him to in some way possess her body and live on in her.
Looking back this seems very relevant to a Sith history filled with apprentices who have a habit of murdering their masters. So while it is possible that Darth Sidious is the first to really figure this out, it seems more likely (to me anyway) that in the distant past some Sith Lord figured this out and has mastered the art of using the inevitable treachery of an apprentice to effectively attain immortality. If that were the case then it seems quite likely that Sidious was in some way possessed when he killed his own master shortly after becoming Emperor (and therefore he is no longer "himself").
In essence, is it possible that Sidious in the latter stories is simply the latest host body for an ancient Sith Lord who has mastered body hopping?
I suppose it's also possible that this technique has been around for a long time but is rarely used because it is difficult to succeed at (example: Sidious failed to perform the ritual himself). In this case Sidious' attempt may be viewed as a last-ditch and ultimately futile attempt to start over. Still, it seems that if there was a ritual allowing a Sith Lord to take over the body of another, someone in the distant past would have had the time necessary to perfect this art.
If all of Sith history could be seen as a matchup between "Apprentice who wants to kill his master" and "Master who has had dozens of past apprentices try to kill him before", I'd bet against the apprentice every time.