for sure! but that's irrelevant to a causal chain that includes "suburbanization", since you're not in the suburbs (in manhattan at least, the walkability does drop off pretty quickly)

another interesting tack: how long did we have cars before we started talking about a widespread mental health crisis? is there a more parimonious explanation, like a different event that is located closer to it in time? perhaps smartphones or the internet?

I think you are too focused on one problem caused by cars. Even if they didn't cause mental health problems due to isolation (seen most prominently in suburbia), they cause enough other problems to warrant pushback.