"Hermione is autistic-coded so it's ableist to call her annoying" is such a self-involved nonsense take that it's barely worth engaging with, but one larger thing is the use of "-coded" being wrong

If something is coded as something (historically, queer), it's authorial intent and implication circumventing the inability to say it explicitly. In the Superman cartoon, when Maggie Sawyer is in the hospital and an unnamed lady is there holding her hand, that's queer coding

Because Maggie Sawyer in the comics is a lesbian with a partner, but they weren't allowed to say that outright in the cartoon. That stated intent is important

Nowhere, to my knowledge, has JKR said anything to the effect of "yeah Hermione is intended to be autistic." If people are reading the book and going "wow Hermione seems autistic," that's a personal READ of the text, which is very different

Personal reads, especially from places of marginalization, are good and important, but they don't supersede the text. Everyone wants Bucky to be gay in the MCU but it's not in the text, and the authors explicitly said it is not in the text.

So it would be very silly, if someone was like "I think Bucky is annoying because he's dark and brooding," to reply "actually that's a homophobic opinion for you to hold." Same principle applies with Hermione

Elle Woods from Legally Blonde is another character who is often read on Twitter to be autistic, but is not especially a know-it-all. A lot of this stuff is more revealing of people's projections than anything else

Anyway, coding is implication, reads are inference. Sometimes the former leads cleanly to the latter, often the latter arises without doing the former. At the end of the day, overidentifying with fictional characters is something to probably avoid or at least be chill about