There is another irritating problem with the idea of omniscience: it contradicts the attribute of omnipotence. If God knows the future with infallible certainty, he cannot change it— in which case he cannot be omnipotent. If God can change the future, however, he cannot have infallible knowledge of it prior to its actual happening— in which case he cannot be omniscient. (This is similar to the issue of in what sense, if any, God can be said to have free will. Does God know his own future decisions? If so, how can those decisions be free? Perhaps God does not make decisions. If so, how can the idea of volition apply to a being with no decisions— and hence no choices— to make?)

Smith, George H.. Atheism: The Case Against God (The Skeptic’s Bookshelf) (pp. 74-75). Prometheus Books. Kindle Edition.