There's realistically fewer than twenty metro areas in the US where the majority of commuters could rely solely on biking and public transit for everything. Twenty might be generous, even.

That may be true, but you don’t have to rely on biking for “everything.” Some biking is better than no biking.

I live in a small college town a couple of miles from the college. I walk, run, or bike to work nearly every day. But I am not a purist about it. We have a snowstorm forecast for tomorrow so I am going to drive (my EV). Would it be better for the environment if I walked? Probably? Does one trip really make that much of a difference though? Probably not.

I think there are likely many many places where people can walk or bike to some of the things if not all of the things. People really should do that more (not the least reason because biking is wonderful). Biking to the grocery store is mostly impractical for me as it is many miles away. But that’s ok! I am doing other things.

Since the pandemic passenger car miles, airline miles are back at pre-pandemic levels.

Transit use is at 80% of pre-pandemic levels.

https://ti.org/antiplanner/?p=22722

Farebox recovery ratios have consequently become even worse.

The new US government is also presumably not going to fund much transit expansion.

It'd be interesting to see if more people work from home on a given day than use mass transit to get to work.

It's also pretty similar in Australia at least and probably in more places around the world.

There is a positive spin on this: the majority of Americans already live in or near dense urban centers. If we had solid public transportation only within these centers and to adjacent suburbs we would eliminate most car trips. That's bot much physical area to cover.

Depends on what you consider "in or near".

I live "in" a major American city. Well, a reasonably major Midwestern city. It's roughly a third the size of Rhode Island. It has half a million people in it.

still rubber so still microplastics?

Less!

Unfortunately a bicyclist on the road will be exposed to far more tire microplastics than drivers in their enclosed cabins with filtered and recirculated air.