
This might just be you reading in to it, especially since there isn't a given diagnosis for either character.
Without having vocal fluctuations like I would in person, please understand that what follows is not intended to be mean– just frank: having been recently diagnosed is probably giving you a hypersensitivity to autistic traits and you are likely analyzing characters for these, just as you would go back through memories to look for indicators of autism in your past.
Everyone has a trait or two that might be connected to autism, but 1, that doesn't guarantee the character is autistic, and 2, a lot of the social-related traits are just there to set up polarizing characters who have different ways of communicating (IE, we get to trope of miscommunication and then realization and then make up sex).
The trend you might be seeing may actually just be a new set of tropes developing, like a stem of the tsundere trope.

Yeah I do think it's a bias, though there were a few cases where they show flashbacks of the person being diagnosed with something, just never what the diagnosis is (I think it was the case for Dohu but I may mistake it for another manhwa since I've been following the weekly updates and may have forgotten some parts or mixed them up)

I agree that @KrB might be reading into this but also to be fair most ppl in arts/audia-visual/media fields still would rather have the very stereotypical (although not necesserily wrong) views of autism/neurodivergence, and the canon character depicted will always be "very far " on the spectrum.
And this MC with the MC of the bl "Semantic error" are VERY much autistic coded (without it being severe). I woulnd'nt say there is a trend tho. But I absolutely do not think its a reach to read them as neurdodivergent. And I really mean just dohu and the MC of semantic error (who also has an obssesion for trucks lol which is adorably stereotypical)not random shy+socially inapt characters.
Also sometimes author does that yk, kinda like how they introduce non white characters without ever ever mentioning a single non white ethnicity or even stating that they're not white. You just understand they're not white through the writing.

The issue i have is that this assumes a lot for the characters, which the author may not be intending. I don't think that autism is the reason for the character personality types: one look on the 'dere types wiki' leads me to kuudere, which are distant people. This trope is basically "introverts also have hobbies"
i'm not necessarily saying there is a trend in general, just among what @KrB might be reading currently. Semantic Error is a lovely manhwa, but I read that ages ago, with numerous characters from different stories in between.
Also, if an author wants to write a story about a character with a certain trait, it gets addressed at some point; this is often in a flashback where that character has some conflict related to the trait. (NOTE: especially if the author is trying to romanticize that trait, leading me to conclude that autism ≠ new sexy) Without any direct mention of autism or neurodivergence, I'm inclined to believe that the characters are just following a common trope.

I'm sure you are right, I see your point honestly but I really wouldnt know cuz this is just not a phenoemenon i'm seeing personally through what I'm reading.
I was kinda making a connection between how autism (and honestly id rather just talk about neurodivergence cuz its less specific) in real life is perceived and how that translate in fiction.
People are already very dismissing of autistic traits that are easily masking/ non severe autism even when we now know that a lot more people are on the spectrum. So it's a bit silly to assume an author would kow better while creating characters. They might get inspired from that quirky kid they were with in high school (who was just neurodivergent and they had no idea lol)
And to me, a lot of time when in media there is a common intepretation massively shared in a fandom it is most likely the situation I described rather than just ppl reading too much into it.
And to comeback to the introvert detached trope (that to me is absolutely nothing like neurodivegence really but maybe to op it is who knows..) I feel like is just cycling trends? so far only "tops" were allowed detached and cold/introverted personalities and now bottoms have that too ig... I mean eventually certain tropes wears out so new one comes in. But in a few years it will change again? idk
I don't know if it's a bias because I only got a real diagnostic not too long ago but I feel like autistic characters are all the rage lately - is it just me? (not that I'm complaining in Dohu's case because he feels pretty accurate to me, though it seems like he never went through the adapting phase - my sister says it's a thing that mainly goes for autists raised as a girl/woman but I would expect that every autist that is not intellectually affected would try to fit in since society doesn't exactly give us a choice in that matter)