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.