You’ve said that Satan didn’t know God planned on Jesus being put to death for our sins or he would have done everything in his power to stop it. Isaiah 53 is a prophecy of Jesus’s payment for our sins, so how is it possible that Satan didn’t know God’s plan of redemption prior to the Crucifixion? Didn’t he read the Bible?
Remember, the Jews were already God’s people and that’s who Isaiah 53 was written to. But when Jesus went to the cross He went for the Gentiles as well, and that’s something Satan never expected.
In 1 Cor. 2:6-8 Paul was speaking to gentiles, saying that God had kept that part secret and none of the rulers of this age understood it, for if they had they would not have crucified the Lord of Glory. The phrase “rulers of this age” refers refers to Satan and Company (2 Cor. 4:4, 1 John 5:19).
By opening the door to salvation for the Gentiles, God had made it possible for every human on earth to escape Satan’s grasp.