Thank you for rambling. It is so good to know I am not alone in that area.

Before I take my turn. I want to clarify something in this comment from your post.
“… to me it seems there was more to it than just eating a fruit from a tree, of course God would be upset with his children for disobeying him, but then to send his children along with the tempter out of the garden to remain in sin ever since is hard for me to understand.”
You are so right that Adam’s sin was more than just eating organic fruit from a special tree. Genesis 3: 6. Eve’s response to Satan’s temptation: “The woman saw that the tree was good for food, pleasing to the eyes, and desirable for gaining wisdom…” Wisdom here refers to the total knowledge of God. Knowledge of all good and all evil would be godly knowledge because what else is there besides good and evil.
At this point, I have to point out that Catholic teaching places full blame for Original Sin on Adam. Eve did commit a personal sin of disobedience when she ate the fruit; however, it was Adam’s personal sin of disobedience which shattered their relationship with our Creator.
Yet, God so loved Adam and Eve and us, because we would be their descendants, that the Second Person of the Blessed Trinity assumed human nature, purely without any sin attached to it, so that in Adam’s place He could be obedient and thus bring about salvation and the great graces of the Sacraments.
So that I do not misinterpret you, I want to make sure that you are keeping in mind the Sacrament of Baptism. Sometimes, because it is so long since my Baptism, I overlook the fact that Baptism erases Original Sin. What does remain is a wounded human nature which is inclined to lust of the flesh, greed, and wrongful pride. We can get so bogged down with Original Sin concept, that we fail to look up to Christ hanging bleeding on the cross. Here is where He infinitely atoned for Original Sin. He literally opened the gates of heaven.
As you mentioned the tree of the Knowledge of Good and Evil, I agree that most people wonder about it. Adam and Eve did have intelligence and free will. What is often missing is the Catholic information as to why this tree played such a crucial role in the creation story.
Now I am rambling and I win because I am rambling back to your first thoughts about needing a deeper meaning of sin.

I wonder if it would help if we keep Original Sin, committed by Adam-- what is the smilie for ha, ha,-- separate from our own personal sins.
In both modes of logic, deductive (philosophical) reasoning and inductive (scientific) method there is plenty of work going on behind the scenes. Accepting the fact that we are personal sinners is a good place to start because then the Good Shepherd can pick us up and place us close to His heart. Then we can question God.
Note: there is still a lot of “behind the scenes” work, questions, and answers in both our posts and the previous posts.