Great game, really nicely made!
I've seen in the comments you talking about the issue of this being a solved game. Like you said, that's not terrible (as it isn't true for all modes), but I would humbly suggest that 3X3 + turn start isn't a great default setting, since it can be beaten by player 1 with classic tic-tac-toe play. That kind takes the special out of this game.
It might make more sense for the default to give player 2 some advantage, like letting player 2 pick all pieces or all except triangle.