Content Warnings: none
I'm calling these "readings" or "interpretations", not "headcanons" (because it's not just a personal-gratification me thing, it's a way of making sense of what's in the text) or "theories" (because it's not about being "proven" right or wrong.)
Also- I'm going to try and go past just "Here's why I read this character as autistic" and go deeper, into "Here's what this story, with an autistic character, is about- how it feels, what it says, etc."