Yeah, I agree that having a secret communication channel between the DM and players is good because it goes deeper than just meta gaming: there's also meta meta gaming.

As in you hear a piece of information that your character would have no way of knowing and this piece of information makes the correct tactical option obvious. It might not have been as obvious before, but now that you know, you can't unknow it (at least not without an even more severe disruption to the game). So does that mean you can't pick that now obvious option to avoid meta gaming? What if your character probably would have chosen that option anyways? Same thing for trying to do something that would reveal that information to your character, would your character have done it without the information? Should you just pick a bad option now because any good option is meta gaming?

I don't think there is a good solution once anyone knows about the information. Hell, even your barbarian's decision to not say anything could be considered meta gaming because you were doing it in response to how the other players were acting and justified it afterwards just like they are doing. Avoiding the meta gaming option is still meta gaming, it's just from a place of not being able to help but meta game.

It's like playtesting magic decks against another one of your decks alone. Sure, you can see some things like how well the mana ramp works, how big of a threat you can get on the board relative to your opponents, but when it comes to interactions, you know exactly what spells you should counter or ignore, what might happen if you choose to block or let an attack through. There's no tactical surprise or bluffing, which can both play a big role in the game.

When I DMed, I liked to have some rolls from the players ready ahead of time, because I found even "roll a spot/listen check" gave away too much information on its own. Pass or fail, it was a signal to start doing some active searching because there's something of interest in the vicinity. So instead I'd just use the early rolls and cross them off my list as the players made passive sensory checks and only mention anything if the roll was high enough.

Then notes can be passed with the information to those who know it, plus extra nothing notes sent from time to time, maybe with a promised reward if they don't say it's a nothing note so the meta gaming that results just wastes time and discourages people just reacting to notes.

(Split it up into another comment since it's a different idea).

Another thing that DMs can do is punish meta gaming with things that go against expectations. Like maybe some secret doors are actually the release mechanism for some damgerous monsters that act as security when someone sounds an intruder alert. Or the listen check is to see if you can hear the siren's song in the distance as you pass a nesting area.

Maybe the pressure plate is connected to a power source and system to bring the facility the players just entered online, turning on lights and opening doors that are otherwise locked when it's in mothball mode because the wizards who built it assumed the secret entrance would provide enough security. So while it looks like a trap, it's just some home automation that would make everything easier. Then if they skip the "trap", gotta have a scene where they return with someone else who does step on it to leave them wondering if they made a mistake or if they did it the more interesting way.

I need to find a group one of these days, it's been too long since I've played a tabletop RPG and I was a naive power gamer when I last did, so I'm curious about playing a game without min/maxing.

Though the best game I've played was with a friend who wanted epic shit like in Devil May Cry. There were no real rules, there were rolls but pass or fail was more of a vibe check than anything specific because the more you described a cool action in detail, the more likely it was to succeed. It was pretty awesome and fun.

For context, DMC features epic scenes like a man-sized entity fighting and beating a skyscraper-sized titan, blocking bullets with swords, and I can't remember if this is actually in one of the games but even if it isn't, it kinda shows the level they are on, but I think there's even at least one scene where a character uses bullets as stepping stones to get within sword range of someone firing down on him from high up.