Free will is not about being unpredictable it is about making choices freely.
If it was impossible to predict which way rocks falls it would not make them have free will.
Would you say "that human do not have free will because I can predict his actions" and then say "Now that I gave this human a dice and mind controlled him in always following the result of this dice I can not predict the actions of that human (because I can not predict the results of that dice) and so he do have free will"
I mean saying free will is about not being predictable would mean that you would consider some humans are lacking free will during short moments because you can over short moments have quite accurate predictions of his behavior(Example: you gave that human a hat and he is in a culture where it is considered polite to not use the gift until you left and so you know this human is not going to wear the hat until you leave).
Free will is about having choices and not about being unpredictable.
Omniscience is about knowing everything.
So it includes knowing what would be the future if you do X or Y so being able to act does not makes you less omniscient.
It also include knowing every false thing and every true thing.(which basically means it is not very informative)
And of course if you are omnipotent you can remove omniscience from yourself: you would just stop being omnipotent because you would be unable to remember everything but omnipotence never says you have to stay omnipotent.
Future do not have to be predetermined for someone to know the future: ten year later there was only one future for ten years ago so no matter which way it was obtained there was only one future for ten years ago so if we take an infinity of people and give them each a different memory of the "future" in such a way that all combination of possibility is included then necessarily one of them have the future that will be the only true future ten years later.
Unless you go around and say there was multiple pasts but did you ever see someone seriously say "past is not predetermined in fact there is multiple potential different pasts none of them being more likely than the others" even through it is symmetrical it is much rarer to see people truly believing the latter than seeing people believing the former.
If you say free will is the ability to foil omniscience then there is no omniscience in the first place if someone have free will since omniscience is not "knowing everything unless something prevents you from knowing that thing" because else you can say every human is omniscient since with the latter you can say that "limited capacities of the brain" and "limited ability to obtain information" and "unreliability of the memory" are the things that prevents knowing stuff outside of what you know and that in fact you are omniscient with those three limitations.
Or maybe you meant "nothing ever had free will" which is something I can agree with if your definition of free will is about making choices that can not be predicted.
*Forbidden to think about phoenix wright and then turn a phoenix into a wight and send it in court to defend the accused.(and turn everyone into wights)