I find it odd that you quoted me to make the post that you have made here, as my post is about it being good for a DM to let players regulate their character knowledge - specifically bringing up a scenario in which the DM trying to step in and regulate for the player results in the amusing while frustrating exchange along the lines of
DM: "You can't do that, your character doesn't know that fire kills trolls"
Player: "...what do trolls have to do with anything? All I said is that my character jabs the monster that encroached upon our camp with a burning log from the fire he was just tending. Doesn't matter what the monster is or isn't or what my character knows or doesn't know about trolls."
Because the DM has gotten distracted by worrying why the player picked a particular action for their character, when that almost never actually matters.
I was just quoting you for the good example of the sorts of problems that might come up when the DM has to worry about whether or not their players are regulating their knowledge, and doesn't have to worry about if their characters do regulate that knowledge.
The situation I find myself in that seems different than a lot of others is that I
do care that the players play their characters with appropriate knowledge, and that in general
I am the one who decides what is appropriate knowledge in my setting, but that the characters are willing and able to regulate their character knowledge according to those assumptions for themselves, so there isn't a hassle over it.
I really enjoy the more or less default accumulated lore of D&D, and don't like to change it, so the methodology of changing lore so the players don't know the truth doesn't appeal at all to me. At the same time, it breaks my immersion significantly, and reduces the immersive significance of chosen ability scores, skills, and other knowledge granting traits, when monster knowledge is based on what the player knows out of character rather than what the character knows, (it's no different than combat skills or Strength to me), so not having a wall between OOC and IC knowledge doesn't appeal to me either.
(I then tell him or her to please stop asking questions and DO something.)
You've mentioned this technique before and I find it an interesting concept. Do you have a play example or something you've written that would illustrate how you do this better? (Not in relation to knowledge, just the general concept.)
And, of course, no matter what, I'm always telegraphing the monster's resistances, vulnerabilities, immunities, and notable traits and attacks. The troll roars at the brazier and kicks it across the room, sending the hot coals flying, or takes a noticeably circuitous route to get at the wizard so as to avoid the campfire, for example. Any player paying attention should have a reasonable chance of inferring that the troll is especially fearful of open flame. Failing to make this effort to telegraph threats makes it a "gotcha" and I'm not okay with that.
As I a player I like to occasionally find myself in those situations. It's not an unpleasant gotcha for me unless it was pulled off poorly. I generally GM the exact same way I want my GMs to do it. This might not be exactly the same as how particular players would like it, but then again I'm an introvert who enjoys spending my recreation time with people as similar to myself as possible, so I'm not concerned so much about appealing to everyone.
On the other hand, some of the telegraphing you're talking about is proper descriptive framework. But if there is no way to tell from looking at it that a mezzoloth is immune to acid, and no player has an appropriate skill, language, race, proficiency, backstory, etc, that would allow them to know that, then I'll let players waste their acid attacks on it until they figure it out. It provides a greater sense of player agency for me, and a greater sense of accomplishment and acquired power (knowledge is power) when they finally learn what they did wrong and don't do it in the future.