The Sequels in now way undue Halo 3. Halo 3 itself literally sets up Requiem, not only that, there was an established number of rings in Halo 3 that isn’t retconned at all between Halo 3 and 4. Bungie definitely left with a sense of closure, but really Halo has as much business continuing as God of War or Call of Duty. The Halo universe had some of the densest lore I had ever seen before Halo 3 even came out. For reference, this game takes place on the most discussed Halo ring in the franchise among fans.