None. It's not a good plot twist. Even the Truman Show didn't use it as a plot twist, but as a premise. If the story was engaging without the twist, then it's a gut punch to suddenly pull the rug and say "gotcha! The plot was meaningless!" If the story wasn't engaging, then you didn't get far enough to see the twist.
That's true; I don't mean that Death Note or any other show would literally become a better show with such a plot twist unless it was a show I didn't like in the first place. I guess rather than "improve" I meant "would be kinda funny/interesting to think about". I didn't mean to imply that it was used as a plot twist in the Truman Show.
One kind of interesting twist on that is Fincher's The Game. It remains unclear until the very end of the movie whether the main character is in a convoluted game where people are pretending to conspire against him, or an actual conspiracy using the game as cover.
I would disagree with that being a plot twist, though. You're aware of both possibilities from very early on, and the idea that it's real appears later than the idea that it's not. It's hard for it to be a twist when people keep directly telling you what the twist is going to be before it happens.
Eminence in Shadow, as that is the reverse of what was originally going on before just kind of becoming a completely ordinary isekai. Having the tables be turned would be kind of fun
Anime; the one thing that gets us closer to each other and brings us together.
All spoilers must be tagged!