Good apocalypse-centered novels? Preferably has no romance or very minimal romance? NO HAREM. Male or female protagonist.
Lord of the Mysteries Doctor plague (has romance, but only happened later on, on chp 400+. And no harem) Dominion's End (josei) Soul of Negary Stagnant Water of Apocalypse Tales Of The World Devouring Serpent (it's a snake, so no romance)
Earthlings are Insane - city is teleported into parallel world and is regularly plagued by monster intrusions.
Why are Lord of the Mysteries and Soul of Negary apocalyptic novels? They are certainly good, but where is the apocalypse? Doomsday Wonderland There is a parallel planets earth. And on every planet earth at some point there comes an apocalypse (monsters, global warming, radiation, flooding of the planet, etc.) and people who survived the apocalypse on their planet teleport to another apocalyptic world, and then to another, and etc. That is, the MC experiences many apocalyptic worlds.