Nextdoor I think was an attempt at that, but it turned out that its mostly a place to talk about fears and potential problems and strangers in the neighborhood rather than bringing anyone together, for anything other than trading stuff.

I think its one of the downsides of the multiculturalism is that the common denominator in terms of culture is smaller - becoming more frequently that you just straight up don't talk to neighbors because you don't trust their motives or beliefs. As a 30-something fairly liberal queer person, I'll have only very light and shallow conversations with my elderly neighbors, because I know they're in their house with Fox News on all day, and would vote for people who'd take away my rights any day. That doesn't mean I don't help them load heavy groceries out of their cars, or offer to help with something every once in a while, but there's this big barrier of culture and especially what is "acceptable" between us.