You can read c/autism and post comments there without joining anything at all.
I’m surprised it’s asking you for an ‘invite’, though. Never seen that. I’d suggest sending a note to the listed moderator. Just click ‘send message’ on their page.
Lemmy is kinda confusing, but it’s worth the hassle. (:
In five paragraphs you’ve summed it up well, and provided an easy, handy rule — what they do matters, not what they say. Not sure I’ve seen it said more succinctly. Sincere kudos, smart stranger.