The probability of the opponent folding doesn't matter. The goal of bluffing in modern games is so that optimal players are indifferent in their decision (no matter how they play, you can't lose money). And because this is a zero sum game, if you can't lose money then you win if the opponent makes mistake.

You only need to know the probability of the opponent folding so that you can deviate from the theoretical optimal strategy to win even more money if they are a biased player