Also, not flattening Kyiv wasn't about what the international community would allow. Because if they did it, sanctions wouldn't be any worse than they are and there would not be a military response to it. Just outrage. Nor was it a matter of air defenses. Ukraine didn't have most of its air defenses in the beginning. The Russian air force has largely stayed out of the war- using less than 100 planes when they have a few thousand at their disposal. It is one of the more interesting aspects of the war. American style shock n awe would be an extensive air campaign for days or a week before even committing ground forces. The lack of Russian air force involvement is something people can speculate about. And it also meant they never truly achieved air superiority.

No, not flattening Kyiv is more about hiding the war from the Russian people and Kyiv is so historically important to Russia it would almost be like bombing St Petersburg. Kyiv is the foundation of the Russian state. If Kyiv was being destroyed and the Russian people knew about it, the popularity of the war would dramatically change. The same largely also applies to Odesa. Every other city, though, was fair game in their eyes.

And it wasn't just about air forces, Russia got within artillery range of Kyiv at the beginning of the war.