Shenzhen is not nearly "almost-all EV" city. There is a lot of wealthy people and almost none of them drives EV. You can see all expensive cars are ICE (blue plates).

Modern ICE cars emit almost no sound or emissions. Its not 70s with black smoke coming from exhaust pipes.

You can take any densely populated city with almost none EV vehicles (say Tokyo) and you can hear birds and air would be very clean.