Seinfeld asserted in an interview with Jimmy Fallon that he did not seek permission from Kellogg for using their product names and characters but he would enjoy being sued.
Max Greenfield's character "Rick Ludwin" shares the name with real life Rick Ludwin, a long time NBC executive who backed Jerry Seinfeld during the creation of the sitcom "Seinfeld" and Ludwin was the one who kept on fighting for "Seinfeld" when other NBC executives didn't believe the show would fly with a greater audience.
Bob Cabana (Jerry Seinfeld) is given apparently bad milk to sniff by milkman Mike Diamond (Christian Slater), asks "What's the expiration...?" and as he passes out Diamond says, "July Third." This is based on a joke Seinfeld did in his standup act, in which the cow that gives the milk tells the dairy its expiration date, and Seinfeld had the cow saying exactly that date, "July Third."
When the mascots storm the Kellogg's building, Hugh Grant's character is costumed as a parody of Jacob Chansley, the Capitol rioter known as the "QAnon Shaman."
Jerry Seinfeld wanted Sir Daniel Day-Lewis to play El Sucre, as a parody of his role in There Will Be Blood (2007). Ultimately, Day-Lewis was not approached, and the role went to Felix Solis.