@Cliff1975 I just saw your message and wanted to offer sympathy for your DS. How awful for him and for you too, watching on the sidelines and feeling powerless to help.
Has he joined any structured activities/ societies and made any connections through those? Did he get to choose who to be nearby in his accommodation? I can't remember what subject he's studying, so am not sure of how much structured academic commitments he's got. Does he connect with people at supervisions or lectures etc but not have any contact with people outside of those times?
Like my DS1 and DS2, he'll have been in the Covid cohort where during the first year, there was very very little possibility of social contact with others and if, by coincidence, you didn't find yourself in the same 'household' as like-minded people, then that was it. has he lived in college for all three years?
My DCs have met a very wide variety for people from lots of different backgrounds in their time at O & C, probably far fewer people with money than just ordinary people. Nobody seems to know or be that interested in who's got what kind of background and it doesn't seem to make any difference. So it's possible that your DS just hasn't met enough people generally or maybe he goes to a college with a cohort who just happen to be either really rich or struggling on bursaries?
It's not too late for your DS to meet and connect with more people. DS2 for example, only at the end of last year, got more friendly with someone he'd barely known, through a shared activity (rowing) and some interesting conversations and DS1 just last week, had lunch with an acquaintance and a nice long walk with them too but hadn't really known them beforehand, except through a wider group of friends and acquaintances with a shared activity.
Sheer repetition of the same activity each week 'accidentally' can lead to friendships of different levels. Colleges are all different too of course. DS2 has a very friendly and sociable household this year, none of whom were actual friends beforehand but they've tended to do things like meals and pub trips together. DS1, by contrast, is in a corridor composed of a pre-established friendship group who keep to their group, usually don't speak English anyway but will say Hi in the kitchen and that's all. His friends have come from one person he'd already known in a higher year, at the start who then introduced him to their own friends and who are now DS1's friends.
Your DS won't be the only one who rarely speaks to others and possibly, especially the case with male students. Can your DS join some activities that put him regularly in contact with others in a way that at least gives him some social contact a few times a week? I think the main thing is that it's really still not too late for him to make connections or friendships with his peers, so i hope he doesn't give up. If he's feeling low, of course, it's harder to do so but that's why structured activities are so helpful.
I hope things improve for him soon.