Alpha gamer is a type of player in cooperative games, who effectively makes a decision for another player. In this question I am asking how to deal with a 'soft' version of this player archetype, who does not make the decision per se, but is quick to point out what he would do.
In RPGs, this often manifests during combat encounters, where one or multiple players, who oftentimes are more experienced than the one making the turn, tell them what to do. They can be quick with probability theory calculations and tell them how do deal the most damage. They can be quick to point out a tactical possibilities to exploit, like a squishy target without cover.
GM: That's all, right?
Player A: Yes, I end my turn.
GM: Ok, Player B, it's your go now.
Player B: Sure. Hmmm...
Player A: The bloodied Lizard Rogue next to you has the lowest AC and didn't Disengage, if you attack him, you'd probably kill him.
Player B: That's right! I attack the Lizard Rogue.
While such behaviour is desirable when the player making the turn asks for it, some players have a habit of announcing those kinds of decisions whether anyone asks for them or not, sometimes approaching the encounters, especially combat ones, as a cooperative puzzle to solve - that's why the term from cooperative board games seemed applicable to this case.
Such behaviour, if frequent, can effectively hamper the players on the receiving end and take away their agency. While I would personally want all the players to make their own decisions and only ask for help when they want it, I understand that some players like to have an always-on guide. However, 'soft' alpha players can effectively command the game whether they themselves notice it or not, which I feel can slow down the roleplaying development of newer players.
How can I prevent that kind of player from disturbing the rest?
In some time, I am to GM a game in which I know that players have non-homogenuous RPG experience. I have played with all of them at different times and know that some of them engage in alpha gaming, at least sometimes, unconsciously or unwittingly. I would like to gather some input from more experienced GMs how to handle this problem, were it to arise, before it happens.
I do not feel that full-on cooperation is a bad way to play RPGs. However, the table participants in their private conversations with me said that they want to make their own decisions in RPGs and at least some of them are vocal in criticising some cooperative board games where this problem is very apparent. As we did not face alpha gaming of such magnitude in our RPGs yet, I am not sure whether the players would be able to solve it by themselves.
In summary: How should I handle a player who very often, maybe unwittingly, chimes in with not bad or even optimal solutions to given problems, even if it's not his decision right now?
While there are already questions about bossy players, I feel that the problem described there is of greater magnitude than this here (there, a player effectively takes control over a game), and as such, needs separate answers, even if a subset of them is applicable here.