When the bikers gang pursues the mayor's Twi'Lek majordomo, one of them crashes through a painting of Jabba the Hutt. This is art by Ralph McQuarrie created for his Star Wars: Episode VI - Return of the Jedi (1983) portfolio, but edited so Luke is not present in the picture.
When Boba Fett mentions he's ridden beasts ten times the size of a Rancor, he is referring to the Paar's Ichthyodont he rode during his first on screen appearance on the planet Panna Prime in the The Story of the Faithful Wookiee (1978) segment of The Star Wars Holiday Special (1978).
Boba Fett's bacta tank appears to be placed at the top of the large tower next to Jabba's palace. This is Alkhara's tower, named after the criminal who owned the palace before Jabba, and who took it from the B'omarr monks who used it as a monastery. These monks removed their brains for enlightenment and had them transferred into modified BT-16 perimeter droids. One of these 'spider droids' is seen roaming outside the palace at the start of this chapter.
The Rancor Keeper mentions Rancors are used as mounts by the Witches of Dathomir. These Rancors and the Witches first appeared together in the 1994 Legends era novel "The Courtship of Princess Leia" by Dave Wolverton. The Witches of Dathomir would go on to be featured in various story arcs in Star Wars: The Clone Wars (2008).
The character Peli Motto, who first appeared in Chapter 5: The Gunslinger (2019), along with several of her Pit Droids, is seen in the flashback walking the streets of Mos Eisley when Boba Fett arrives in town after leaving the Tusken raiders.