There’s no uniformity in these methods.
Oftentimes, these stories have fewer moving parts which mitigates the need for large outlines.
Brainstorm random ideas that you like, get ideas from dreams, etc. See if you can combine the ideas somehow. It’s the writing equivalent of improv acting.
Just experiment a lot. Write cool scenes, cool characters, etc. and just see where they take you. Let a compelling story flow out.
There probably will be a lot of rewriting and “wasted” pages that you don’t end up using, but that’s okay because it’s what you had to do to generate the story.