Free will v predestination, like most theological disputes, is solved by Christ — the God man, who is both man and God. Fully Sovereign, while also fully man who obeyed the will of the Father, and not partially but completely man.
Predestination debates go back even before Calvinists v Arminians, even before Augustine v Pelagius, the Essenes v Pharisees had this exact same debate while Christ walked among them.
And notice in each of those conflicts, one group inevitably feeds into the other (usually a reactionary movement to perceived fatalism). They’re flip sides of the same coin (unfortunately with many falling off into heresy).
You cannot read Scripture, especially the epistles, without seeing a rock solid case for predestination, while simultaneously, even in those same epistles, seeing a rock solid case for man’s agency. Both are affirmed in no uncertain terms. And in our modern worldview this is seen as a contradiction.
The mistake is to put human reason above God, as if human rationality is above God. Or to put God within time as many Calvinists are unfortunately want to do. He (Christ) is the author of reason and time, and transcends both, while also revealing truth to us.
Christ solves the seemingly impossible free-will v predestination puzzle through his life, death, resurrection, and ascension into heaven (as a man) — which strongly affirms both His Sovereignty and affirms man’s agency. This is something no other religion can solve, including secularism.