What I mean is books that have characters live in settings that are, in-universe, fictional in some way or the like. I don’t mean books that have adaptations in other mediums
Preferably the story has at least one of the following: the world has its own laws of physics; shows how the world works; explores the setting’s implications; explores how it affects characters; or the world is under threat.
Thanks for your help👍
Closest thing I can think of is The Never Ending Story. The protagonist enters a book that is essentially a gateway to the world of all imagination.
The next best thing I can think of is something like Dungeon Crawler Carl where the setting is essentially a deadly reality TV show that takes the form of fictional worlds. Or things like Discworld with it’s narrative causality. Or Orconomics which makes fantasy tropes and rpg conventions explicit in the setting through satire, in which financial institutions are inflating the adventuring bubble through loot backed securities.