Von Neumann proved that there exists an unexploitable strategy for any zero sum game, where playing that strategy gives you the best possible outcome if your opponent knows your strategy and can play perfectly against it. Poker players refer to this strategy as "Game Theory Optimal". It is not necessarily "optimal" in the sense of making the most money in real life, EG if your opponent always folds to big bets then you should bet big more often than a GTO strategy would.
Over the last 15 years or so high level poker strategy has increasingly focused on approximating GTO play, and people are moving away from any type of exploitative play, whether that's psychological tells or adjusting to weaknesses like an opponent folding too much. So a GTO player actually will bluff quite frequently, but it's due to the math indicating that it's an advantageous spot to do it, not because of anything he's observed about his opponent.
That said, there's still room to adjust to exploit an opponent, and the weaker the opponent is the more profitable it can be to deviate from "correct" play.