Consider this: a godlike pool player is using a pool table with no holes. The surface and sides are frictionless, and there is zero energy loss when the balls bounce off of the sides.
He breaks, and the balls are in motion. He is a savant & can track the positions and velocity of every ball on the table. He knows the laws governing the motion of the balls explicitly and can extrapolate to predict the future position and velocity of any and all balls on the table at any time in the future, with perfect accuracy.
Now consider the universe as a collection of mass and energy operating under its own laws. A god could know the exact position & velocity of any particle in the universe. (Of course, we can’t do this to even one particle, as per Heisenberg’s Uncertainty Principle, but it can be imagined that a god could.) He could then extrapolate forward in time, and know what Would Be then.
The universe isn’t like a pool table. But it does have its own set of rules, and even action on a personal level involves chemical processes and interaction with the outside world, which while far too complex to predict (or model) by mankind, a conceivable god could do so.
If a god knows exactly what will happen in the future, how can there be free will? If every action we take is a result of pre-existing conditions & the rules governing their interaction, then free will is merely an illusion.