I agree with your point about car oriented suburbs, but I’m also not convinced living in cities is necessarily social particularly in America.
I lived without a car for 5+ years and I didn’t find it led to spontaneous interactions. I think there’s other cultural and socioeconomic factors at play here.
I live car-free in a dense Canadian urban center and it doesn't lend itself to social interactions with strangers, indeed. Going outside means being assaulted with loud, dangerous car traffic and an absence of places where strangers can, for lack of a better word, "loiter".
If we want to facilitate impromptu social connections we need our streets to be pleasant and and safe from cars so that people want to stay around. Trees, benches, playgrounds, flowers and fountains. This is nothing new, it is how towns have been built for centuries until we sacrificed them in the name of cars and of economic output.
I lived without a car for 5+ years and I didn’t find it led to spontaneous interactions. I think there’s other cultural and socioeconomic factors at play here.