One of the basic laws of ecosystems is: the biomass of a herbivore must be 10 x smaller than the biomass of the plant they eat, and likewise 10 x between predator and prey.

In a city, the biomass of humans is huge. Unless the city is a literal space ship powered by its own fusion reactors and utilizing direct chemical synthesis to create feedstock for edible yeasts and bacteria (skipping nearly all plants and skipping absolutely all animals)... without that, we can pretty much forget about a city feeding itself, or it will be an extremely large and flat city which some would call "countryside" (or an energy-intensive city with multi-storey artificially lit greenhouses).

The space ship scenario - skipping all animals, skipping most plants and getting the goods from the simplest possible food chain - of course assumes a rather uninteresting menu driven by necessity. People wouldn't be satisfied with such a menu, if they have the possibility of eating more diversely.