Middle school is just the worst, man.
facts!
Mainstream vs not seems like a tough choice. Getting used to the real world (as that's not changing to accommodate them) is a hard road, I would reach out to other neurotypical kids, parents or advisors you work with, and see what worked for them. Everyone has their own limitations, so one size definitely doesn't fit all.
What about activities/clubs, that sometimes can help find 'like-minded' friends? Often you can work independently in the group, so not have to mingle constantly.
They have robotics, film, chess, D&D, Model UN, art and many others. not sure that's going to solve all the problems, but might find something that get's him engaged and psyched to go to school
There are also some private schools that might fit the bill like
https://thesycamoreschoolva.org/but $$$$
Middle school kids are the absolute worst. That's pretty universal