America is super big and super stretched apart
Perfect for long-distance rail travel. Just get in the train, wait X minutes to get to the next town over, and get out. It's literally how the west was colonized in the second half of the 19th century.
What makes America bad for public transit isn't that the nation is spread out, it's that suburbs are a death knell with how spread out they are. I honestly don't think there's a way to make suburbs self-sustainable short of quadrupling the US' population so you can get decent density even there. Sort of like the SF Bay Area except actually building medium density housing instead of having >8 people to a low density home.
More realistically, the suburbs will probably have to be scrapped. It's not like those homes were built to last, anyway. Just don't replace them when they need to be condemned.
As for there not being enough greenery in cities, that's just a matter of choice, isn't it? Pedestrian boulevards can be lined with trees, building facades with ivy, public parks next to apartment blocks, etc. etc. Almost all the toxins in western urban areas today are from car tire dust and exhaust. Just ban motorized personal vehicles except mobility scooters and e-bikes, and most of what you seem to hate about urban areas can just go away.
Could you explain why?