Unused footage of Carrie Fisher shot for Star Wars - Il risveglio della Forza (2015) was incorporated by digitally removing the background and superimposing it elsewhere. Visual effects were used to change her wardrobe and add gray to her hair so the footage would match her appearance in Star Wars - Gli ultimi Jedi (2017).
When George Lucas originally laid out plans for 12 episodes, then reduced it to nine, he said that C-3PO and R2-D2 would be the only characters to appear in all nine. This proves to be true: Anakin Skywalker and Obi-Wan Kenobi, the only other characters to appear in every movie of the original and prequel trilogies, did not appear in the sequel trilogy. Anthony Daniels is the only actor to appear in all nine episodes. C-3PO also appears in Rogue One: A Star Wars Story (2016), Star Wars: The Clone Wars (2008) and most of the animated series including Star Wars: The Clone Wars (2008) and Star Wars Rebels (2014).
John Williams stated that this would be the final "Star Wars" film for which he would compose music.
During the massive crowd celebration scene in Pasaana, C-3PO says that this event happens once every 42 years. This is the time between the releases of Guerre stellari (1977) and Star Wars - L'ascesa di Skywalker (2019). This is also a reference to Douglas Adams's use of the number as the answer to "inexplicable" phenomena in his writings.
As per Star Wars tradition, someone or something "has a bad feeling about this". This time, it is Lando Calrissian (Billy Dee Williams).
John Williams: The bartender in the cantina on Kijimi. His character's name is Oma Tres, an anagram for "Maestro." He is surrounded by 51 objects that represent the 51 films for which he received Oscar nominations up to that point.
Jeff Garlin: As a background alien on the Resistance base. The Visual Dictionary identifies this character as 'Junn Gobint'. He is of the 'Mythrol' species, the same as the first bounty seen in Chapter 1: The Mandalorian (2019), who was played by Horatio Sanz.
J.J. Abrams: [cast] casting Greg Grunberg as Snap Wexley, a role he had already played in Star Wars - Il risveglio della Forza (2015) as well.