Ask Science Fiction, Who Would Win, The Maw Installation, and similar discussion boards for in-universe questions about fiction.
For those who aren't familiar, Ask Science Fiction (more accurate parsed as Ask Science: Fiction) is a board for asking and answering questions about fiction from an in-universe perspective. Questions and answers don't necessarily have to be role-played, but they should assume the internal logic of the universe in reference. Answers from an out-of-universe perspective ("George Lucas didn't decide that Darth Vader and Anakin Skywalker were the same person until later") are against the rules, though there's some allowance for media that's super-meta and can't be answered otherwise.
Who Would Win is a board for posing hypothetical scenarios, often but not exclusively about fictional characters or factions. Think "Who would win in a fight between Superman and Batman?". Evidence in the form of references to specific canon media is encouraged.
The Maw Installation (and similar places like the Daystrom Institute for Star Trek) is essentially Ask Science Fiction, but specifically for the Star Wars franchise. I find that boards like this can encourage interesting world-building that makes the original text feel richer, as well as more in-depth critique of the text as media.
I'm sure some of these exist in some form in Lemmy, but I'm still looking for them!
Lmao you fucking numbskull