This probably isn’t all that uncommon, but a modern urban fantasy setting would be a fun one. I had the idea for a campaign once that took place in a sort of very-near-future fantasy setting where there was a world-ending event slowly creeping across the planet, and the players were a group designated to go to destroyed areas, find survivors, and stay behind to ensure those survivors made it out, but they end up accidentally discovering exactly what was happening in the process. Whether or not they could stop it depended on the players actions, and there was a hard in-game time limit after which point it would have become impossible, neither of which the players would have been aware of.

Essentially, picture a radiation-free nuke going off and turning all living things within the shockwaves reach into purple crystals in a major city. Then it happens again. And again. Seemingly at random all over the planet. No one can figure out why, or how to stop it, so they decide the best course of action is to evacuate as many people as possible to a space station in orbit. The players objective was to A: get people to the escape ships and B: protect those escape ships

Either that, or a hard sci-fi set in a single solar system, or even just limited to 2 or 3 planets, kind of a “the expanse” deal.

Edit: as a side-note, one of my friends and I sometimes just come up with concepts for DnD characters, even if we don’t have any campaigns to play them in, and one time we both independently coincidentally made tiefling characters with guns meant to be played in a wild west setting. Hers was based on the concept of love and was a love cleric, and mine based on the concept of revolution, though I can’t remember the class. We decided that if we ever played them in the same campaign we’d call our inevitable team-up “The Union” and have a sort of Bonnie and Clyde dynamic since both had criminal backgrounds