I bought Apocalypse World 2E. Between my (admittedly nascent) familiarity with FitD and this video, I think I have a pretty good idea how the basic mechanics of PbtA work. However, I am still kind of at a loss at exactly what the MC does for "prep". I think it is mostly jotting down ideas and formalizing threat between sessions, but I am not entirely sure. So the first thing I could use help on clarifying is what the role of the MC is in PbtA games is specifically in regards to how much or how little to "prep."
NOTE: I understand that you don't prepare adventures, with plots and things. That's not my question. My question is more about how much world building and hook slinging do you do, as compared to, say, a sandbox D&D game. Sometimes the text seems to suggest that the amount is "none" but other times it tells you to use your "prep" to ask and answer questions.
Lately, I mostly run West Marches-style open-world sandbox D&D 5E games but there were a few years where I mostly ran/played various PbtA games. Dungeon World, Masks, Monster of the Week, Uncharted Worlds, Spirit of 77, etc.
Most don't require the full world-building you'd expect from a purely homebrew D&D game. They are typically very player-focused in world-building. Players are regularly encouraged to add details to the world. Most PbtA games have questions in character creation either on the sheet or in the book for the referee to ask to help fill out the character and the world. The referee is also often told that when questions about the world come up to ask the player of a character who should know...and have them decide. So very much collaborative world-building by design.
For things like NPCs, factions, etc...it's about the same as most sandbox D&D games. You're supposed to, as the referee, create factions, NPCs, etc to populate the world. But that prep is supposed to be focused on the characters. You create NPCs that your PCs will bounce off of, or gravitate to, or otherwise strongly react to. In some iterations of PbtA the referee is supposed to specifically create NPCs that will come between the PCs and cause problems. But players create a lot of NPCs as well. Their backstory and character creation picks, depending on the PbtA game, can generate any number of NPCs that might or might not show up in game. Anything from a cousin who works at the local bank on up to entire aliens worlds. Same with factions, basically. For example, in Masks one of the playbooks is the Bull (strong fighter-type superhero) and they were created...think normal person kidnapped and experimented on to gain powers. The faction the did that is out there. The player can have a lot of input in creating that faction.
Hook slinging is about the same, I think. But you're generating your hooks differently. You're mostly pulling form the characters, the collaborative world-building, and the fronts you've designed. Fronts being the events you want to feature in a game. A lot of the drama from PbtA games comes from the characters themselves and their interactions with each other. I know some PbtA games have a much looser stance on PC groups, but I haven't played many of those as it's too awkward. I prefer the specifically team-focused PbtA games. So you start the game, typically, with a relationship web of sorts between the characters. Like in Masks. You have a few backstory question to answer (just about your character), then you have relationship mad-libs. You pick some of the other PCs to have a shared history with to keep things cohesive but also filled with drama. For example, again from Masks. "X is your love" and "Y is your rival." Or "You and Z pulled an illegal stunt together" or "You're trying to impress A with your antics."
Very often the advice is "poke the PCs at the start of the game and simply react as this sets off a chain reaction." And most PbtA playbooks are built to service that style. Lots of in-built drama, hooks, NPCs, etc for the referee to use against the PCs. Not to screw them over or pull the carpet out from under their feet, rather to introduce drama.
Most PbtA games are laser focused on creating drama for the PCs to wade through. So whatever prep or hooks or world-building you do as the referee should be focused on that drama. "This time it's personal"? Nope. Every time it's personal. Basically, if it doesn't poke at least one of the PCs it doesn't belong in the game. Some PbtA games are more or less laser focused on drama. But as a generalization, I've found it's true. Not to put too fine a point on it, but if you think of PbtA games like soap operas you'll be most of the way to grokking them. Not bad, hammy melodrama...but if you're going to have a traitor it should be some PC's relative or best friend...if you're going to introduce resurrection (for example) the players should find out about it by having someone their PCs love or hate coming back from the dead. All that stuff most D&D players are trying to avoid by having the tragic "everyone I've ever known is dead" backstory...yeah, that's where most PbtA games live and breathe. Prep that stuff.