Autism

Autism coded characters are 100% a thing - I'd go a step further and say it's possible for a character to be Autism coded without the author realizing. Ultimately, all characters are based on experience (either the writer's own, or the experience of other writers they're influenced by), and I think it's fairly common for writers to draw on a particular archetype, inspired by someone they know or a character they've seen elsewhere, and implement that archetype without realizing that their inspirations (and hence their derivative creation) are autistic.

One of the most famous ones is Abed from the TV show Community, who supposedly wasn't initially written to be autistic, but when everyone pointed out that he was it led the showrunner to realize he himself was probably on the spectrum as well.

I've seen people suggest that Peridot from Steven Universe is autistic coded as well (although I'm not sure it makes sense for her to be literally neurodivergent, since she is an alien rock and doesn't have actual neurology).

I feel like I had a bunch of examples of characters who are autistic coded but not confirmed to be autistic, but they're not springing to mind right now. I've thought about this before because a bunch of them are great characters that I resonated with before even noticing their autistic traits (or mine). Someone already mentioned Judah Mannowdog from Bojack Horseman.

Oh, I've seen people say Lilo from Lilo and Stitch is autistic coded, and I guess I can see it. Also, obviously Sheldon Cooper is a negative portrayal of autism that the creators will never admit is autistic because then they'd have to admit he's a mocking caricature of autism.

There are some great characters from one of my favorite shows who I'm pretty sure are autistic, with differing presentations. But, while I'm happy to identify as a fan of that show, and happy to identify as autistic, I worry that identifying as both at the same time is playing into some negative stereotypes about both groups. But one of the characters is really into rocks and the other is really into kites. Iykyk.

I briefly googled autistic coded characters to try to refresh my memory, but have only included characters I have personally previously formed opinions about, since that seemed to be what you were asking for. But if you just want a bunch of discussions and lists, googling "autistic coded characters" will get you a lot of different takes.

In general I feel like autistic coded characters are often better representation than explicitly autistic characters, because when a piece of media explicitly labels a character as autistic, they can often lean into making Autism their only personality trait, or even make it a selling point of the entire work. Autistic coded characters have the luxury of being an actual person that happens to be autistic, instead of a walking billboard for the writer's research on neurotypes.