Sherlock is a TV series with a devoted fanbase (- this is an understatement, obviously.)
Clearly, he's also a character who speaks to people who clamour for someone like them on their TV screens.
Whether it's a good or a bad thing that this is all headcanon instead of canon, is debatable.
Headcanon, aka headcannon, head canon, and other variants, is something which fans accept and treat with the same due reverence as canon, but which is unofficial.
-Example: the Marvel movies without Ant-Man still have Ant-Man in them, you just can't see him.
Canon is the official material of the fandom. It's the things that are actually mentioned in the book, TV series, etc. It's therefore the basis of the fandom.
-Example: Harry Potter is a wizard at Hogwarts.)
On the one hand, the headcanon allows a multitude of identities to find resonance with Sherlock and his character. On the other, a canonisation of one, or several, of these under-represented identities would make a huge difference for the diversity movement.
So, whether your headcanon is for an asexual Sherlock, or an autistic one, (or hell, maybe both, I'm not the headcanon police,) there is probably a fic out there for you.
This week's fic might just be it.
This fic features a Sherlock on the autistic spectrum, written by an author who is also on the spectrum.
It's a little clunkier in terms of prose than the last fic I recommended which had an autistic Sherlock, but it's still well worth the read.
I definitely enjoyed the informed perspective involved, and found the discussion of ADHD medication (something which displayed knowledge of the topic,) quite interesting.
I also liked the Johnlock aspects of this fic, as all too often depictions of autism seem to suggest that non-neuro-typical people don't have any emotion and/or can't feel love. Which is not true.
(Fangirling note: Johnlock is a romantical/sexual relationship between Sherlock and John Watson.)