Rian Johnson went from directing a massive movie in a part of the newest Star Wars trilogy to a much smaller production, an original story with a unique take on the classic whodunit. While both movies had incredible casts, that's about the only thing that Star Wars: The Last Jedi and Knives Out have in common, that and the approach of writer/director Rian Johnson.
While one movie was part of an on going franchise with established characters, and the other was a brand new story with completely original characters, Rian Johnson says that he didn't approach writing either of them any differently, because both stories were still brand new, and both still had to work in their own way. According to Johnson...
I don't really think in terms of universes, or in terms of creating worlds or whatever, that's not that interesting to me. The only thing that’s interesting to me is story, and the story specific to whether you're writing a Star Wars film that's part of a three movie trilogy or a ‘original thing’ like Knives Out, you're still telling a story that's new to the thing that you're doing that has to work within the context of that movie.
Rian Johnson does have a point. Even though Star Wars: The Last Jedi was part of a trilogy, that might have included characters that we know, the movie itself was still a brand new creation that would take those characters to new places. Creating the story itself isn't necessarily any different or easier simply because we know who Luke Skywalker is. That's not to say that the story wasn't in some way shaped by those existing characters, but at the end of the day every script has to start from scratch and you're certainly not guaranteed that a sequel will be better simply because the characters are known by the audience.
Rian Johnson specifically tells THR that he doesn't get excited about the idea of creating a universe, but does get excited about creating cinematic experiences for an audience to have, which is why the story is the most important thing.
Rian Johnson has more stories he'll need to create in both of these franchises now. He has a sequel to Knives Out that has been given the green light that will see the return of Daniel Craig as detective Benoit Blanc, and he's got an entire Star Wars trilogy he's planning to write. This will actually flip the script slightly since the Knives Out sequel will include a familiar "universe" while the Star Wars trilogy, while it will be part of the larger franchise, is supposed to be something entirely new dealing with characters we've never met before.
Of course, based on what Rian Johnson says here, this fact won't actually change anything about the movies he's about to start writing. In the end, the goal will be a strong story that excites an audience the whole time they're in the theater.