I would be hesitant to draw that correlation. IMO cars give you more access to third places, not less. With a car one can cover far more ground in a given 30 min drive after rush hour died down probably in every city in the world, than what one can cover in 30 mins walk and transit ride (especially when transit schedules might favor a commute into the central part of town vs some off peak trip to a random corner of town).

Say what you will about the ills of the car, but it takes a lot of specific context for them to emerge as the worst option of transport from an individual perspective. Really most of the cars ills are from their collective harms, something most can't appreciate as a tragedy of the commons sort of failing.

There's no shortage of third places in the American suburbs, you just have to drive to them. I'm sympathetic to the argument that walkable third places are better third places because I lived car-free in New York City for a decade and enjoyed many of them. But living in the suburbs or exurbs doesn't inherently mean you don't have access to shared communal spaces.

If I believed there is a crisis of isolation in the United States and degradation of community, I would first focus on more recent technologies, say ones introduced around 2007, than on technologies introduced in the early 1900s.