Is there a Game Theory Optimal solution?

This would mean that there are strategies (if the game is played with a fixed set of possibilities such as fold, 1/3 pot bet, 1/2 pot bet, pot bet, 2 pot bet allin) where both player A and player B know each other strategies and they can play that strategy perfectly meaning that none of them can deploy another strategy that would make more profit against the other.

Do we know that this is solved and what the theory for the solution is or do we assume that the computer just calculates all possibilities and then finds the perfect strategy. Or do the current programs use some theory as to come to a local optimum strategy. Or do we use an AI constructed program to play against itself to come to a best strategy (meaning that we actually don't know if it is the Game Theory Optimal solution) just a damn good 'AI' solution much like the best chess bot which can beat each human player.