This sort of debate always struck me as nonsense. If our actions are not derived of our own free will, but just exist as a small part of nature, then if you follow that thread far enough you’ll understand that all reason and truth would also be invalid, being just the effect to some coincidental cause. This incidentally would render theories about the subject of free will invalid as well.
Thus if there is no free will there is no way for us to know it.
Thus if there is no free will there is no way for us to know it.