Look at solo RPGs! They’ve been around for a bit, but really came into their own during Covid.

I’m a big fan of the Ironsworn/Starforged/Sundered Isles series, which is a fully self-contained RPG you can play yourself, with other players (and no GM), or with a GM guiding people through. Many of the “moves” you make during play let you define the world and plot as you go.

On the other hand, if you have a game system you want to play already, you might look at the Mythic Game Master Emulator. Both of these have systems for generating stories and worlds on the fly, but Mythic is designed to plug into an existing RPG, while the Ironsworn series works some of those details into your character.

Ironsworn is free (the other supplements do have a cost), while Mythic looks to be about $15. Also, the YouTube series Me, Myself, and Die has playthroughs of both, so you can see how they work!

(Edit) I forgot about narrative games! They’re a bit of a different beast, more rolling for prompts and deciding how you respond, less rolling to-hit, as I understand it. Thousand year old vampire is the big name in this space.