There is a very simple way to have "walkable-cities" without any central planning or any of that 15-minute, smart-city crap. Just allow residential and commercial zones to mix. Allow people with big enough houses to run shops in them.

I know a lot of local stores and restaurants that were renovated from former houses. Just remove the walls between the kitchen and living room, and have the bedrooms be employee offices then you will have enough space to run a store.

You can take that one step further. Why not have a house with a store attached? A garage can be converted into a small shop or you can have the other side of a duplex be a store. Japan has tons of houses with stores attached. There are even apartment building with something like a 7/11 at the bottom.

See? A simple solution that doesn't involve demolishing entire towns and rebuilding them or building expensive railways that would require evicting a bunch of people and destroying their homes just to make room. Car-dependent cities are a result of central planning, not the other way around.