The big Lebowski kind of has a sequel in The Jesus Rolls

It’s a popular theory that a lot of Tarantino movies take place in the same universe, and other of his movies are movies that exist in that universe, like Kill Bill may be the pilot that Mia Wallace starred in. I don’t believe any of that is outright confirmed, but again kind of a sequel if you buy into that theory.

There was a Napoleon dynamite cartoon series made at one point if you want to count that

Forest Gump was based on a book, and there was a sequel book made- Gump & Co, and I never read it myself but I’ve been told that the sequel book is actually more of a sequel to the movie than to the original book