This is a core premise for an Inform 7 game, entered into SeedComp 2023 (https://seedcomp.org/)
The idea is that the PC is an actor in a play, and can switch between being 'in character', where their surroundings are the reality of the play itself, and 'out of character', where they can see the stage, props, and audience. In the story part of the premise, the PC is an understudy for someone who never gets sick, so they didn't bother learning their part--but then they got called in anyway, and now have to improv their way through the play, based on their extensive knowledge of theater and preternatural ability to fully inhabit a character and do what comes naturally.