[kosta50]

He created this world, and in that act, every single person’s destiny was fixed

The only thing that is fixed (ordianed) is that all men shall die once (cf. Heb 9:27), whether righteous or not.

The moment of our death is not necessarily fixed: "I have heard your prayer, I have seen your tears; behold, I will add fifteen years to your life." (Isa 8:5):

Just as St. John of Damascus says: not everything God (fore)knows has been (pre)determined by God.

[xzins]

St Damascus is avoiding the obvious.