"I'm autistic and I feel isolated, almost like I'm a different species, so I'm going to write a story about someone who literally is a different species and that's why they don't fit in!!!"
Okay, cool, sounds fun. But are you prepared to deal with the resulting statement you're making that different people shouldn't live together?
Are you going to provide specific problems that arise from this scenario that make cohabitating an actual problem, (temperature incompatability, dietary requirements that can't be met, overstimulation from having different levels of hearing or vision) or is it just going to be that the problem is they're different kinds of people, and that means they shouldn't live together?
If you want to write being a completely different species as a metaphor for being autistic, you need to make sure you're not accidentally arguing that segregation is a good thing.
Because you can very easily slide from point A (being autistic is socially isolating because you're different from everyone else) to point E (different people shouldn't live together at all because there's no way to be happy unless you're around people who are exactly like you)
How to avoid this with your "different species as a metaphor for autism" stories?
Assuming your setting has many sentient species, have very specific problems that prevent specific different species from living together.
Do not make it a general problem of "no species can live together"
Show us different species living together, even when there's no "real" advantage to doing so (like living in a port city with lots of trade passing through). Make cohabitation a casual thing that lots of people from lots of different species do.
Show us accommodations that species make for eachother when living together. Species X has incredibly sensitive hearing that can cause them pain? Species Y adapts their local dialect to soften what would normally be loud pronunciations to convey specific meanings. Species A has strict mating seasons where they lose control of themselves and start attacking anyone they view as a rival? Species B, and anyone else who doesn't want to participate in the fighting, moves to another site for the season and gets to come back in a few weeks to everything being nice and tidy.
Make it so there are specific problems that specific individuals have with certain situations, not the entire species at large. Even with your metaphor being about being autistic, you should still have some characters, of every species, who are literally autistic. And include other neurodiversities too, like mental illnesses.
And while we're at it, give people physical disabilities too, and not just as a result of cohabitation with the "Well species J are mermaids and Species K are land-mammals, so if you think about it, Species K are disabled in the water" thing. Have characters who are amputees from birth and injuries. Have people with allergies. Have people with migraines. People who are deaf and blind and hard of hearing and struggle to see and any other physical disability you can think of. Your species shouldn't be monoliths, not mentally, physically, or culturally.
???? IDK
Just try not to let your "being autistic is like being a different species! I must find my people!!!" thing turn into "segregation is good and are we even really sure those other species are even people"? thing.
because it's a lot shorter of a slide than you think it is.
And again. cannot stress this enough. You also have to show literal autistic characters existing in your setting in these various cultures. Even if it's a fantasy setting so you make up another word to use instead of "autistic".
Otherwise your story might accidentally have the moral of "autistic people are literally not human and there's something Wrong With Them™ that we need to try and fix or else we have to cast them out of society altogether".
Don't let biological essentialism ruin your fun autistic story.
