I've certainly had negative interactions on Lemmy and elsewhere.
With reddit… I'm not blaming you, but communities are how they are. Different subreddits are different.
If you're posting in /r/autism and experiencing that, then I'd perhaps suspect the issue might be more on your end - how you're presenting yourself. That said, there are a lot of toxic places on reddit, for sure.
I'm essentially no longer on reddit, but I was there since 2009. I still say things that get downvotes. Mostly silly jokes that whoosh over peoples' heads, but sometimes just randomly. It might be my fault some of the time, but it's definitely just the way it goes. Sometimes I make a comment and expect downvotes but get upvotes; and sometimes expect upvotes and get downvotes.
Also, "reddit" doesn't tell anyone anything. Users on the site certainly do. They're individuals deciding what to say, just like here - I am not Lemmy telling you any of this, I'm me. And if I was on reddit talking to you, I'd still be me.
That said, before I almost-completely withdrew from participating in reddit, I browsed /r/all on old.reddit using RES to filter out so so very many toxic subs (and subs I wasn't interested in).
There's plenty of neurospicy people on reddit (I was / limited-still-am one).