Some areas I have seen have surprisingly high forage abundance interspersed among buildings and patches of concrete. A given city / urban setting can very greatly from another. I have also seen the chickens roaming streets. It is done, but community needs to be accepting of it.
Community is the key point there! When you move out to the country and have acreage, you tend to lose some of that community aspect... I miss my neighbors from the city... I traded backyard produce across my “keep my cats in my own yard” lattice fence with my Chinese neighbors that spoke as much English as I did Mandarin. Bartered some maintinece tasks for loaning tools to others, and knew almost everyone in the block by name. Thread sorts of communities are becoming a thing of the past though... I think that we bought in a “rougher” working class neighborhood had a lot to do with our experience.
I was also seriously considering starting a community raised bed vegetable garden on the city boulevard I was expected to mow... but never quite got around to the guerrilla gardening I wanted to do on it.