Yes, Ralbag does say that God does not know (certain aspects of) the future. See Book III of Milchamot Hashem for his full treatment of God's knowledge. The basic idea is that God's knowledge of man's future actions is limited by man's free will. God knows what man will likely do, based on his makeup and the celestial influences, but man has the ability to choose to act differently from what God could have "predicted".
Ralbag mentions this concept a number of times in his commentary to the Torah. For example:
- Genesis 18:20
- The Sixteenth Lesson there
- Genesis 22:1
- The Sixth Lesson there
- Exodus 3:11
- The Twelfth Lesson there
Here is my full translation of the second example:
The sixteenth lesson is in ideas. And it is to teach us something amazing of God's knowledge of things, which was hidden from all [my] predecessors whose words have reached us. And it is that that which God may He be exalted knows of actions in this low world is independent of what man [actually] does. That is that He knows the actions of people that are fitting according to what was prepared for them from the day of their creation, based on the celestial causes that God may He be exalted placed as guidance over the human species. [However,] human choice rules over this arrangement of their actions based on the celestial causes. And it is therefore possible that what people actually do is different from what God may He be exalted knew [they would do] based on the arrangement of their actions. And this is because He knows their actions from the side in which knowledge of them is possible, and that is the side in which they are arranged and quantified. But on the side in which they are contingent there can be no knowledge, for if we suppose that knowledge of them is possible then their contingency cannot be upheld. And therefore it says metaphorically that God may He be exalted saw whether the people of Sodom and Gomorrah actually did the evil that He knew from them, because it is possible that what they had done was different from what God may He be exalted knew from them. And we have explained this topic of God's knowledge of things in Book III of Wars of the Lord. And we explained there that this view is necessary on the basis of philosophy as well as on the basis of Torah.
In another post, I argue that Rashi might have held a similar view.