What is the name of the secret Sith planet visited in The Rise of Skywalker?

The story behind the answer

The hidden Sith world in The Rise of Skywalker is the storm-wracked stronghold in the Unknown Regions where Palpatine and the Sith Eternal assemble the Final Order. It’s reached using a Sith wayfinder, a relic that encodes treacherous hyperspace routes. This distinguishes it from the distractors: Korriban is the ancient Sith homeworld in Legends (called Moraband in canon); Mustafar is the lava planet of Vader’s duel and castle, seen briefly at the film’s start; and Dathomir is home to the Nightsisters’ dark magick, not a Sith base.

Context: The film ties this world to millennia of Sith secrecy, portraying a cult, vast shipyards, and ritual chambers that visualize the Sith’s “Rule of Two” legacy evolving into a hidden empire poised to return.