It is true that omniscient means knowing everything, however the future of what choice someone makes is not knowable and doesn’t count as part of everything because it didn’t happen yet.
No, not how it works. If he doesn't know a thing, any thing at all, he's not actually omniscient. Stop trying to bullshit your way out of it, you're not fooling anyone.
From the wikipedia
“Other means of reconciling God's omniscience with human free will have been proposed. Some have attempted to redefine or reconceptualize free will:
God can know in advance what I will do, because free will is to be understood only as freedom from coercion, and anything further is an illusion. This is the move made by compatibilistic philosophies.
The sovereignty (autonomy) of God, existing within a free agent, provides strong inner compulsions toward a course of action (calling), and the power of choice (election). The actions of a human are thus determined by a human acting on relatively strong or weak urges (both from God and the environment around them) and their own relative power to choose.[4]
A proposition first offered by Boethius[5] and later by Thomas Aquinas[note 2] and C. S. Lewis, suggests that God's perception of time is different, and that this is relevant to our understanding of our own free will. In his book Mere Christianity, Lewis argues that God is actually outside time and therefore does not "foresee" events, but rather simply observes them all at once. He explains:
But suppose God is outside and above the Time-line. In that case, what we call "tomorrow" is visible to Him in just the same way as what we call "today". All the days are "Now" for Him. He does not remember you doing things yesterday, He simply sees you doing them: because, though you have lost yesterday, He has not. He does not "foresee" you doing things tomorrow, He simply sees you doing them: because, though tomorrow is not yet there for you, it is for Him. You never supposed that your actions at this moment were any less free because God knows what you are doing. Well, He knows your tomorrow's actions in just the same way—because He is already in tomorrow and can simply watch you. In a sense, He does not know your action till you have done it: but then the moment at which you have done it is already "Now" for Him.[6]”