Free will is incompatible with omniscience. People really want it to work, but it doesn't.
Free will is observer-dependent, and is short for "I can't predict the behavior of this thing". For an omniscient observer, there is no thing that it can say that about.
Free will is not an inherent property of a thing, and that's what trips people up so much.
To ponder it a bit, does a rock have free will? A dog? A human? A super-intelligent AI that we can't hope to comprehend? Why or why not for each step?
The definition above explains it all. Of course a rock doesn't, we can predict its behavior with physics! Maybe a monkey does, people disagree on that. Of course human do though, because I do!
Now ponder what the super-intelligent AI would think. "Of course the first three don't have free will, their behavior is entirely predictable with physics"