You enjoy talking about X, and it makes you happy. It feels good to be with other people when you can talk about X. It would not feel good if everybody else just talk about Y and Z.

Other people like to talk about other things, and it makes them happy to talk about them with you. It makes them feel good around you and like to be with you.

Sometimes, remember to not only talk about X but spend some time asking what other people are interested in, and ask questions about it when they do talk.

I'm not diagnosed as autistic (though I and everyone close to me suspect I am) though I am diagnosed with fairly severe ADHD which leads me to hyperfocus intensely on anything that interests me. It also makes it very difficult to focus at all on things that don't interest me. I have always had a really hard time fitting in, had more than my fair of ostracization, but as an adult now I've realized that what I've gained by being true to myself is a fantastic group of friends who appreciate my true self without any changes to make myself seem more 'normal'.

Children are horrible, spiteful, cruel fuckers and there is kind of no way around that. You are going to have to help your kid weather that storm in a way that doesn't involve stifling their authenticity. Obviously, teach them the importance of basic manners and how to not make a fool of themselves, but you also need to trust that exposure to the awful bleakness of youth will make them more resilient and capable of handling adult life.

Take all this with a grain of salt. I'm a computer programmer, not a child psychologist.

the one thing i wish i had more control over was my interests and fixations. oh how i wish it was fluid enough to direct at-will. alas. i am fortunate in that my primary focus developed into a profitable avenue which makes talking about it part of my job. but growing up i had to learn to be selective and strategic when it comes to discussing some of my other fascinations. along with that, i aim for a 50/50 conversation dynamic while socializing, using active listening and asking any direct and peripheral questions on the subject. while my methods, which i had developed long before i finally received my diagnosis, make for an effective “neurotypical interaction“, they can be quite draining to maintain and do not actually help me forge genuine connections. masking, or knowing how to behave to blend in/pass as neurotypical, is a tool i’m glad i have - but it is not without its disadvantages and long term impacts on my own health and wellbeing.

for some contrast, my younger brother (23) who is also ASD, has been been going continuously hard in the paint for pokémon since his preteens. it makes up 90% of the topics he chooses to discuss, and he has an incredible talent for turning any other topic back into something about pokémon. lol. most of the time the people in his life will humor him, at least for as long as they can. but it’s clear he never picked up on the 50/50 dynamic obligation that binds me in social interactions, nor does he often try to engage anyone on their own level and ask questions about topics he’s not necessarily interested in. in order for him to actually connect, the other person either has to commit to getting all the way on his level or better, have a genuine interest in pokémon themselves.

so pulling from both examples, i would recommend a multip-prong approach. as others have rightfully suggested, try to help your son improve his own interest in learning new things from others by engaging his classmates on topics they enjoy talking about as that can be beneficial for his confidence and comfort around others. but keep in mind that a successful “self-monitored” interaction as observed from the outside may not necessarily equate to a connection between your son and these peers. so at the same time, i would recommend you look for social outlets for your son that would give him the opportunity to talk about his passion with someone else who wants to listen and share with him over it. be it a club or organization or online forum or a single friend, and support his engagement in that and his relationships at school with equal enthusiasm.

hope that helps. cheers!