Yes. Thank you for asking for clarification.
Awesome.
In TTRPGs, it is one way but not necessarily the only way.
No, it's not the only way. But any honest examination of RPGs will reveal we have basically three options. Referee authority. Shared-player authority. Or mixed. D&D and PbtA games are far closer together than apart on referee authority. Games like Fiasco are sold as shared-player authority, but they default to temporary referee authority in places. A referee having authority is how the vast majority of games handle this however, so that should be acknowledged.
One of the things about FKR that gets talked about a lot, for example, is that all the players, including the GM, are bringing their understanding of the world (e.g., Marvel Superheroes, Star Trek/Wars, etc.) to the table. So the trust isn't solely about the GM's understanding of the world, but also the players'. So while the referee may have final say on the shared fiction, it may not be the sole and exclusive say of the GM because this shared fiction is likely being negotiated by the players and the GM.
Hmm. In FKR games the referee is the authority of the game. They are the sole deciding factor in basically every regard. The players are expected to have familiarity with the world, setting, genre, etc, but (as you say), the referee is the final authority. The players are free to play and RP and act in character as much as any other game, but the rules are basically non-existent in most cases almost completely replaced by the referee. The player can create their character, with referee approval. The character can act and think and respond as the player wishes. But as with D&D, the referee is the final say on the fiction. Some referees do give players control of the narrative in places. What's your sister's name? Who's your contact in city hall? Who's your nemesis? Referees and players can collaborate on the setting in the same sense as most PbtA games do at the start of the game. However much more control the players have than that is entirely the purview of the referee.
And to be clear, I do not equate negotiating the fiction (i.e., getting everyone on the same page about the fiction) with MMI.
Nor do I. That's session 0 or pre-session 0 stuff.
Sure, and this is likely why other people in this thread have said that 5e enables MMI or can be prone to MMI. But the language of an adversarial GM is your own contribution to our discussion. It is not mine. I have said on repeated occasions that MMI is not about a Good GM vs. Bad GM or even about adversarial GMs.
A lot of people in the thread seem to equate MMI with adversarial refereeing. It may not be your definition, but it seems to be a common one.
I think that there is a difference between interacting with the GM to negotiate the shared fiction or the GM framing the fiction of the scene and requiring permissions from the GM for the player character's thoughts and actions. I don't think that it's helpful or particularly insightful to conflate these things as being one and the same. Respectfully, if you believe that these are the same thing, then it's doubtful that there is any chance we will see eye to eye on this matter.
Even going to the extreme edge of high referee-authority style gaming, the player is still in control of what their character thinks (barring telepathy, mind control, etc). The player/character has tactical infinity and can try anything. The character's success however is not up to the player. So while they have control over their actions, they have no control over the outcomes. They can certainly influence the outcome in various ways (bribing the guard, stacking the odds in their favor, etc), but not control. The referee narrates the outcome and/or calls for a roll.
But, as I said above, the only way the player has to interact with the world is through the referee. That's just how most RPGs work on a basic level. What the character thinks is up to the player, but what the character sees...is up to the referee. What the character tries is up to the player, but what the outcome of that action is...is up to the referee. Basically, the player controls the character's internal world while the referee controls the external world. The referee is free to cede control over certain aspects of the external world, of course, but is not required to.
As you are talking with me, then mine and yours are really the only relevant ones for purposes of our interactions.
if we look back at what other people have said about MMI...
Pick one please.
then this was never being debated by those criticizing MMI. No one has wanted their PCs to know everything. No one has wanted no mystery to the game or knowledge outside of their character's ken.
People in this thread have argued for knowing things their characters could not possibly know in the name of making well-informed game decisions.
But can I know anything? What can I know? What is permissible for a player to know about player character knowledge or in-game knowledge that isn't GM-gated? Must I ask if I know everything about the world? What is common knowledge? What isn't? What is reasonable for my character to know? Is that really the GM's sole discretion?
Established world. The referee will tell you at some point what fantasy world the game is taking place in. They will generally inform the players of any changes made to the world, if they're things the characters would know and/or if the players assumptions need to be curtailed (for example: FR but no elves), but otherwise rely on player knowledge of that world (or easily accessible books, wikis, etc). So, by definition, what you know about the world is gated by the referee.
Homebrew world. The referee created the world. What does the player know about the world? Whatever the referee tells them. How do you, the player, find out what your character knows about the world...you have to find out from the referee. Either ask or they'll tell you (for example: "what's common knowledge about topic X?" vs "here's the one-sheet of common knowledge for my world"). So again, by definition, what you know about the world is gated by the referee.
Collaboratively-created world. Everyone involved in the design process knows what's in the world. Someone might forget and need a reminder now and again. So the player gets to decide what their character knows about the world.
FWIW, I don't think that any of this is necessarily about an adversarial referee/GM. That seems to be an idea that you are introducing into the argument but that is not what I have said or argued, because I genuinely believe that there are non-adversarial GMs who engage in MMI as well. These may also be the GMs who fudge in favor of the characters.
Then we're back to needing a working definition of what MMI even means.