Freewill in the end means a creature is granted the ability to reject God. If you cannot choose to reject God, you have no freewill. If you can choose to reject God, then you are granted with the freewill. It's almost mathematical (about statistics and probabilities).
Judgment is a process to identify those with God and those not with God. A creature with freewill thus either turns out to be with God (as a result of accepting God and accepted by God, more or less like a marriage between man and woman, both have the will to live with each other in an eternity). or turns out not to be with God (as a result of rejecting God or rejected by God, again more or less resembles a divorce of marriage).
A set of Law which is applicable to both angels and humans is supposed to be used in the Final Judgment to decide who (which creature) can live with God in an eternity (which we call Heaven). The expected outcome is (mathematical probabilities), 2/3 angels will pass the judgment by the degree of freewill given to angels, and with less than 1/3 humans will pass by the degree of freewill given to humans (it is thus a narrow gate).
Satan tried to screw this up by tempting the first lineage of humans, Adam and Eve, to sin such that whoever sinned inside the dwelling place of God will have to be kicked out of the current Kingdom of Heaven. Satan's calculation is, once the first lineage of humans are kicked out of God's realm, Satan is in control of the rest. Not a single human can escape Satan's influence to pass the judgment of Law (which is used on angels) to enter the future and final Heaven to live with God eternally.
On earth (a place outside of God's realm where Satan is called the god of this world in terms of his influence) Satan is trying his best to keep each and every single human under his captivity such that no one (not a single human) can make it to pass the final judgment to be deemed righteous to enter Heaven. He successfully made it so.
So with Satan's effort (by his freewill), God's plan is altered. By the same judgment of Law, it remains the same that 2/3 angels will pass but 0 humans can pass versus the less than 1/3 as planned (a mathematical expected outcome by the degree of freewill granted). In this case, God is defeated as reality doesn't go as God planned (mathematically in logic). Satan expected a win in this case.
Now with Jesus as a justification (God's plan B), lawfully humans don't need to be judged by the same Law as used on the angels. Humans now are judged by covenants instead of Law (the set applicable to both angels and humans). God thus retains the mathematical expected outcome that less than 1/3 humans will be brought to Heaven. In this case, God has the win while Satan is lost due to the miscalculation on the factor that human salvation can go through Jesus by the justification He actively chose to make with His crucifixion on the cross.
So with Jesus' effort (by His freewill), God's plan is not altered. By the judgment of Covenant, less than 1/3 humans will be saved along with the 2/3 angels, as planned (mathematically).
Another misunderstanding is that, as an analogy, earth is a filter securing the cleanness of an aquarium Heaven. Heaven is the aquarium with earth as its filter. However a lot of us have assumed that earth is the aquarium thus question why so much evil exist on earth. The contrary is, earth is a filter thus everything dirty will show up here, such that evil will be exposed and destroyed once and for all through the lawful/legal process of Final Judgment, such that a clean Heaven can be achieved.
It means, in terms of sovereignty, everything is under God's control, in the past, right now and in future.