Board Game Arena

I've gotten the impression that it's whoever meets the goal last gets the Goal first (e.g. if Player 1 meets the requirement on their first plant but Player 2 meets the requirement on their second plant then Player 2 would get 15 points whilst Player 1 would get 11 points), but I think I've seen some situations where this hasn't occured (but I could be mistaken).

If the above is true, what tie-breaks when the tie-breaker needs a tie-breaker?

When multiple players achieve the same goal on the same round, they get it in turn order. The player who chose the action gets the goal first, the next in clockwise order gets second, and so on.
It doesn't matter if you got it on your first plant or second plant, or even when activating the board and tableau. After the round ends the goals are given to whoever completed them in turn order.
Thus you don't need any further tiebreakers for achieving goals on the same round.

Huh can't believe I never noticed that Thanks for the explanation.