The Cause Shapes the World
How civilization ended determines everything about the world your survivors inhabit. A nuclear exchange leaves radiation and mutual distrust. A viral pandemic leaves bodies and immunity hierarchies. A slow ecological collapse leaves a world that is still technically functional but increasingly hostile. A sudden EMP leaves all the technology in place, useless. Choose your apocalypse based on the specific pressures you want to put on your characters and the specific themes you want to explore. Do not choose your cause for spectacle alone. Every detail of how the world ended should generate the specific survival challenges your characters face.