The original claim was that by knowing all, God had predetermined everything. This is not the same as saying that God's omnipotence makes him responsible for all that occurs.

You can't separate those issues. We consider omniscience and omnipotence separately, but they're really both part of God's nature and both are crucial to both issues.

God's omniscience coupled inextricably to his omnipotence mean all things are predetermined by one mind (unless it changes) and all things are the responsibility of God.

To say he can't allow free will isn't to deny God's agency, it's more like the square circle argument; it's addressing a simple logical inconsistency. It's not too hard to understand why God can't make a square circle: it's a linguistic trick using an adjective to create nonsense. It's not really a concept, it's something that tricks you into imagining that there's a concept.

"Free will" and "omniscient omnipotent creator" is the same kind of thing, it's just more complex. There's a concept you're sure is extant, but it isn't really, it's a trick.