There absolutely is uncertainty in chess. Or do you know with certainty that you will win before the game starts?

There is uncertainty about which moves are best, but no uncertainty about what the state of the board is or what will happen when any move is played.

There exists some optimal play for both white and black, we don't know what it is yet, but someday we might and then chess would be truly solved like tic tac toe.

Exactly, we don't know the best play. So chess is uncertain. Whether there is a theoretical best move or not does not make playing chess any more certain if the move is unknown.