The way I see “predestined” is that God predestined all of humanity to go to heaven, have given each individual free will and grace to choose if they want to go there or not.
Predestination on its own is not easy to understand, lot of theology comes into play and into consideration, like Grace, Merit, Justification and Mercy, lot of theologians have struggled with, its not as clear as you suggest of not being omnipotent
