The easiest way to understand the episode's plot twist, and Beppe's convoluted explanation, is to think of it as levels.
There's
Ground Zero: This is the real world, our world dare I say. The actual Joan (played by Kayla Lorette) that inspired
Joan Is Awful to begin with, lives here. In this level, Joan is watching the actor Annie Murphy play out her life. So basically, everything we were watching as an audience, is what source Joan was watching as well.
Then there's
Level One: In this world Joan is played by Annie Murphy, who thinks she's real because she's been coded to believe that. But Murphy's Joan isn't real at all. Instead, she's a CGI version of the real Joan in Ground Zero (IRL). And in this level, Murphy's Joan is watching Salma Hayek Pinault play Annie Murphy.
Then there's
Level Two: In this world Hayek Pinault's Joan is watching Cate Blanchett play her on screen.
Then there's
Level Three: Blanchett's Joan exists here, and she's probably watching another A-list actor play her as well (let the theories run amok of who that might be, I'm hoping it's Meryl Streep).
The levels continue to build off each other to create many worlds within worlds, and shows within shows, but none of them are actually real. Everything starting from Level One is a simulation, the only "real Joan" is the one existing in ground zero. This Joan is the one who shat in a church (
check the episode's post credits to see that scene). This Joan is the one who actually destroyed Streamberry's quamputer. And this Joan is the one who triggered the events we see Murphy's Joan doing throughout the episode.
In Ground Zero, the real Murphy teamed up with the real Joan to stop Streamberry. In Level One, Hayek Pinault (playing Hayek Pinault) teamed up with Murphy's Joan to stop the show. And in Level Two, we can assume that Blanchett's going to team up with Hayek Pinault's Joan to stop the show as well. All levels are just a mirror of things that have already happened in Ground Zero.
While the many worlds of "Joan Is Awful" may be a brain teaser at first —
is it even a Black Mirror episode without one? — the answer is simple when you break everything down. Season 6 of
Black Mirror kicked things off with a great start, and I don't know about you, but it might be time to start reading Netflix's terms and conditions.