“The LORD saw that the wickedness of man was great on the earth, and that every intent of the thoughts of his heart was only evil continually. The LORD was sorry that He had made man on the earth, and He was grieved in His heart.”
The fact that God ended up destroying the entire human race and starting over with Noah implies that God genuinely felt deep regret. The only way to feel genuine regret is if there had been the possibility that things would have turned out differently. This means that God did not know with absolute certainty that man would come to such a pitiful state. I’m not suggesting that God didn’t foresee this as one of many possible scenarios for mankind, but the clear demonstration of regret by God shows that man coming to this shameful condition was not the most probable scenario that God foresaw.