God is good, so man already has knowledge of good. The fall was man setting his knowledge of good as equal to God’s rather than trusting Him.
See this church father:
Even then I’d go farther and say that under that sentence, they would begin to feel the effects of it, such as losing the glory that their bodies once had and noticing the weariness that leads to death.
I’m willing to look at it this way too - that God had already given Adam grace but did not want him to take hold of eternal life through the tree but instead recognize it would be through death, perhaps symbolizing the necessary death of Christ first before eating of the tree in the new heavens and earth @Mark10.45
THEODORET OF CYRUS. What is the meaning of the verse “ Lo, Adam has become like one of us?” Though the devil had declared, “You will be like gods, knowing good and evil,” Adam incurred the sentence of death for breaking the commandment. So the God of the universe said this ironically to bring out the lie in the devil’s promise. Now, God had forbidden Adam to partake of the fruit of the tree of life, not because he begrudged him eternal life, but to check the course of sin. Indeed, death is healing, not punishment, for it checks the onset of sin: “He who has died has been acquitted of sin.” He ordered him to live directly opposite the garden so that he would remember his trouble-free existence and hate sin for causing his life of hardship. [Theodoret of Cyrus, Question 40 on Genesis]
Genesis 3 | Patristic Bible Commentaries
OK - I’ll grant you that it’s 1500 instead of 2000. I haven’t done the math for myself. I was rounding.