I guess since the trilogy is over they're ready to be more forthcoming about some stuff. Fun tidbits from the TRoS Visual Dictionary:
Starkiller:
-The planet that became the Starkiller base is confirmed as Ilum, the kyber-rich planet previously used by the Jedi for thousands of years for the gathering ritual (as seen in The Clone Wars). As many of us expected.
-The small lone star leftover from the Starkiller's destruction is now known as the Solo.
Sith Cultists on Exegol:
-The Sith Cultists on Exegol already existed at least as far back as Return of the Jedi, prior to the deaths of Sidious and Vader. They are believers however they are generally not force wielders on the level of a true sith.
-The cultists longed for the Sith's return and in anticipation began rebuilding a fleet soon after Sidious' death.
-Snoke is said to have been designed by the Sith Eternal Cultists, to train Kylo Ren and eventually to be a test to be overcome, proving whether Ren is worthy of inheriting the Sith legacy. (I assume at the order of Palpatine.)
-Ochi was not an exegol cultist but was a sith lore enthusiast and relic hunter, and enjoyed associating with the cultists.
-Still no explanation is given for the baffling macguffin that is Ochi's blade. Apparently he got drunk once and bragged that he found the wayfinder in the emperors vault, but no explanation is given for why he left it there and made a macguffin blade instead of taking the damn thing.
Wayfinders:
-Sidious and Vader both each possessed their own personal Sith Wayfinder to Exegol. Sidious kept his in the Death Star throne room. Vader kept his on his castle grounds on Mustafar, which is where we see Ben at the start of this movie. (The trees are called Irontrees)
-Luke's Jedi Compass, a prop seen in his hut and also in the Battlefront 2 campaign, is basically the Jedi version of a sith wayfinder. Looks different but same tech. It helped him find Ahch-to.
The Final Order:
-The First Order acted as a testbed for technology later improved upon for use by the Sith Final Order.
-While they are not clones, Sith Troopers receive flash-imprinting and loyalty conditioning based on Kaminoan techniques. Which is more involved than the training that First Order troopers receive.
Dyad:
-The Dyad is an idea that features very prominently in Sith lore.
-The Sith Rule of Two is closely connected to the idea of the force dyad.
-Ben and Rey's dyad connection amplifies their force powers the closer they become.
Misc:
-Maz is who helped Leia acquire her Boushh disguise back in RotJ.
-The design of Obi-Wan's lightsaber appears in the ancient jedi texts, potentially indicating that he based his off an old design.
-The medal Chewie receives at the end is indeed the one that belonged to Han, which Leia was holding at the time of her death.
-That is indeed the Tantive IV. It was found derelict in a hangar somewhere and gifted to Leia.
-After visiting Pasaana with Luke hunting for Sith stuff, Lando liked the people so much he later decided to retire there (which is why he's at the party).
-The briefly seen UA-TT walker is an evolution of the Clone Wars era AT-AP walker.
-D-O is a homemade hobby droid, not a mass produced model.
-Kef Bir is know as the ocean moon of Endor. It orbits the same gas giant as the forest moon. There's also the metallic moon, the dark moon, the patchwork moon, the bleak moon, the ice moon, the rock moon, and the dead moon.
Oopsie:
The VD confirms that it was Ben himself who set Luke's jedi temple ablaze, as was obviously intended by the movies, even though a supposedly canon comic would apparently like us to believe it was actually a strike of lighting (not from Ben) that did it. (Even though comics are technically canon and there's no such thing as C-canon anymore, well...we all know they're still C-canon.)