Didn't Stargate have a show inside the show called Wormhole Extreme or something like that? And Peter DeLuise who directed Stargate was the director on the fake show as well.

Spike Jonzes's Adaptation shows Charlie Kaufman writing the screenplay for the movie in itself.

The Japanese film One Cut of the Dead: I don't want to explain too much, but if you want a movie that takes this concept to the furthest degree then you should check it out.

Episodes (starring Matt LeBlanc as himself) is very much up this alley. It's a show about two British TV writers adapting their big BBC hit for American TV. It's also one of the more underrated shows out there, I don't see a lot of people talking about it and frankly it's excellent.

I thought it was interesting that Modern Family was sort of presented as a reality show, but as far as I can remember, they never showed any of the crew/interviewers.

Not exactly what you asked for, but Dr. Horrible's Sing-Along Blog had a director's commentary track that was also a musical.

One Cut of the Dead is one that comes to mind, you can watch the zombie movie at the start, and then the rest of the movie is the crazy things that went on in the background to make the movie. It's a lot of fun.

Oh, also the Human Centipede trilogy. I haven't seen it, but my understanding is ::: spoiler spoiler the second film has the first one in its universe, then the third one includes the second film and immediately leads up to the first one again :::

The Muppet Movie is all about the Muppets meeting and trying to get to Hollywood to become movie stars. At the beginning and end you see the Muppets in a theater watching their own movie.

Actually a lot of other Muppet content is similarly meta.

The Wizard of Speed and Time is a feature-length indie film about the creator's struggles with creating the original short film that inspired the movie.

Teen Titans Go! To the Movies is about the Teen Titans going to Hollywood to try and get their own movie.

Or best of all, Troll 2, and its explanation movie « Best Worst Movie ».

Synecdoche, New York

maybe? A movie about a theatre piece explaining the life of the author making this show.

Clerks 3 is about Kevin Smith's heart attack and then making of a movie very similar to Clerks.

Wow...meta overload! 🤯 So mainstream is Postmodernist self-reference that it's no longer even recognized as such, it's almost banality. Maybe the owls really aren't what they seem after all?