There’s been an apocalyptic event. Nearly everything’s wrecked. Write about a utopian society there. How did they manage to make utopia possible when dystopia would have been easier?
For reference, a lot of the stories told as part of the Star Trek universe center on just such a society. People do argue that the Federation is actually more dystopian than it first appears, but to me, it has several compelling utopian elements irrespective of the possibility of co-existing dystopian elements.
Trying times can pull people apart, but has often brought people together. Think of how people come together in a crisis. They don’t look at one another as strangers; they see fellow beings in trouble and they care about and for one another.
Quite the fertile ground for the seeds of utopia. :)