Seems like a strange causal conclusion you are coming to. Suburban sprawl has been happening in America for a long time. I grew up in the type of neighborhood you are discouraging 30 years ago. I have lived in high density population and suburban and my experience is interaction is generally lower in high density.

I love Europe and have lived there but you certainly don't get to know your neighbors 3 floors above you in your apartment complex better than you do in a suburban community in Utah or any other state. I think you could make the argument that the smaller the community the more you know your neighbors but the density of large cities discourages that. I doubt most anyone in New York City talks glowingly about how connected the community is in their high density living area. I have never in my life thought of restaurants and marketplaces as particular places for community interaction. I mean sure I see neighbors and we chat when we run into each other at the store but rarely more than a minute or two. Again, that likely happens more in a small town geographically separated from other population centers but those communities are not often in threat to be over taken by suburban layouts.

Are you only referring to communities of SFHs and arguing for smaller lots and homes? No idea but you might have some impact there. I still think there are likely so many other more impactful reasons for less community interaction.