one of my favorite worldbuilding tropes is settings being like post post apocalypse. like the world ended ages ago and life has sprung back and is still chugging along with new understandings and challenges. bonus points if the cataclysm/end times was something eldritch or arcane and almost unknowable in nature. bonus bonus points if the story is told through the environment as most people are so far removed from it that’s it’s just some old thing that happened in history to them.
funnily enough my hard sci-fi world building project that i’ve on and off worked on over the last few years is post post apocalyptic however it does not score any of bonus points because the cataclysmic event was the fall of capitalism and it’s relatively recent history to the canonical current day so the event is pretty well cataloged and remembered.