Are there any sorts of local classes he would try? Exercise, sewing, cooking? A short term class isn’t a long commitment.
Our local recycling center and Salvation army use volunteers. The recycling guys look more social with each other. None of them talk much - okay I’m exaggerating because they don’t talk at all when people bring the stuff in for recycling. They move the recycling materials around and help people unload. But they do stand around together from time to time, I look at them and wish Jeb had that much socialization in his life.
One sister in our FtF had started a monthly group on meetup (?) for her brother. I think it was advertised as for people with brain struggles. They just ate and hung out.