And before you ask:
"If it is myth, then what did Jesus die for?"
The word "myth" does not mean "false" in academia. It means "origin." It only means "false" among people who tend to use it that way in the vernacular. (Like when some people call all soda pop "Coke," even though all soda pop is not "Coke.")
"Mythology" is an ancient genre where writers who did not know exactly how to express facts or truths about the origin of something used tropes common to their culture to explain it. For example, Pandora's Box is a myth that explains the origins of the world's troubles and why human's still hold onto hope despite them all, employing metaphors as a means to explain this.
The narrative of the Garden of Eden is not about Jesus Christ or this sacrifice however. That is a completely different religion, namely Christianity. The Church Fathers admit that their interpretation of the narrative is based upon seeing new meaning into the story, such as they did with Jonah and the resurrection of Jesus, with Jonah being a type of Jesus, and Jonah's coming out from the whale as a typification of Christ's resurrection (based upon something Jesus himself briefly taught).
The original Garden of Eden origin story is about the Fall of Man, but not about original sin. It is about disobeying the Mosaic Law, notably the Jews being disobedient to God, and likely their losing access to the Temple and the Promised Land at the Exile to Babylon. The question is: Why do we sin like this? Because we have been like this since the beginning. It is part of our nature. Like God tells Cain, you need to fight this beast or it will get the better of you.The choice is yours.--Genesis 4:7.
In Watchtower theology, the story is historical fact: it happened as written. No questions asked. And Jesus died to counter Adam's death. It is not a Jewish story. It is a Christian story. End of line.
In nomimal Christian theology, Jesus died as part of his life: God came in the Person of Jesus to experience everything you and I experience from birth to life to death, even unjust rejection--the worst even. God allowed this to happen to him so that we could experience life "in his image" to the fullest. God was partaking of our life by undergoing a death life ours.
The allegorical/mythical understanding of the Genesis story is not required where there is not an exact ransom as demanded by Watchtower standards. For the Watchtower, where there is not a God that lays down His life so that you and I can be "partakers of the Divine Nature" (2 Peter 1:4), the idea becomes cartoonish with literal talking snakes and demanding deities and a Governing Body that sets all kind of weird dates confusing people with perfection and confusion about myths from an old book that don't tell you much about the real world you are living in.
The Jew in me is not necessarily claiming you should or should not believe in one Christian standard or another. I am just reporting on these things.
And thus the meaning of "myth."