Is autism coded characters a thing?

Short answer: Yes

Long answer:
rules:

• no autism diagnosis (excludes Sean Murphey)
• no possibility of autism ever suggested (excludes Gregory House and Regan from inside job)
• no alternate diagnosis (excludes Komi from komi can't communicate who is canonically SAD not ASD)
• must demonstrate an autistic trait, though not necessarily the obvious one (Sprig is here because he experienced sensory overload in a cinama)
• no traits only shown in fanfiction considered (I don't want to be here all day)
• have to be from a show I've watched and I personally have to see it (no Abhed from community, no Catniss Everdeen from hunger games)
• they don't have to be good representation (so I don't have to justify several of my choices most notably Sheldon or Beverly)
• no instances where the author obviously knew what they were doing when they created the character (excludes the Mitchells from the Mitchells vs the machines, but not sheldon because they fell into writing him like that by accident)
• being an excentric genius isn't a sign of autism (excludes Albus Dumbledor)
• being an idiot savant isn't a sign of autism (excludes Forrest Gump)

so in no particular order:

• Myne and Ferdinand from Ascendance of a bookworm
• The entire La clan from Apothocary Diaries
• Luna Lovegood from Harry Potter
• Several Stephanie Meyers protagonists including Bella Swan from Twilight, Wanderer of the stars from The Host and the one who keeps changing her name so it's not worth keeping track of it from the Chemist
• L and Near from death note
• Lios from delicious in dungeon
• Mob from Mob Psycho 100 and Saitama from one punch man
• Saiki K from the disasterous life of Saiki K
• Akun from Aho Girl (also Yoshiko get's an honorable mention for ADHD)
• Star from Star vs the Forces of Evil
• Mabel and Dipper from gravity falls
• Luz from owl house
• Marcy, Sprig and Polly from Amphibia
• Ferb from Phineas and Ferb
• Lilo from Lilo and Stitch
• Peridot and Lapis Lazuli from Steven Universe.
• Papyrus and Nabstabluk from undertale
• Abby from NCIS
• Spencer from iCarly
• Commander Spock from Startrek
• Captain Sam Carter, Dr Daniel Jackson and Thor from Stargate SG1
• Sheldon, Raj, Beverly and Amy from the Big Bang Theory
• A lot of spidermen, though it's strongest in Penny Parker IMO
• Every robot ever put to screen who's name isn't Baymax
• Many, many aliens including some listed above