They made Jessica into a physical fighter, converted Liet Kynes into a black lady, excised the distinctive word 'jihad' to refer to Paul's vision of war. They removed the Baron's homosexuality and sexual perversion and changed his servant boys into (bald) servant girls, etc.
The damage wasn't too bad all things considered, but in Dune 2021's case the source book was not the Bible and it was definitely messed with.