It’s a name that was created for that storyline. Palpatine, much like the term Sith, was used for the OT and its marketing materials. Sidious was treated as his truer name, with Palpatine being more of the disguise.
Not to get too technical, but the name Palpatine was actually first used in the 90’s EU. Before then, he was just called “the emperor”. Either way, the name was much more prominent in the prequels, so I don’t see why using Palpatine can be seen as ignoring the prequels. Those movies never hinted that Sidious was his true name, it was just the nickname given to him by the Sith order. Either name is fine in my opinion.