Adam and Eve eating the Apple was not a sin in this world.
Adam and Eve ate the Apple while still in the confines of Eden. So they brought sin to Eden.
Free Will is why Adam and Eve were able to decide to eat the apple.
Satan did not make them eat the apple.
Satan gave them a choice and persuaded them to eat of it.
They had a choice to eat it or not it.
They chose wrong. Hence sin (going against God's wishes).
The Apple was not an apple.
The Apple is knowledge of good and evil. Which is the knowledge of science basically. If you think about it it's true. Science is knowledge that can be used for good or evil.
Eating the Apple was Adam and Eve rejecting God's blessings, in favor of having the knowledge to procreate, cook, build shelters etc. Because in Eden this knowledge was not needed. God provides everything. A perfect climate which means clothes/shelter was not needed. Plentiful fruit/clean water. No need to hunt/farm or sanitized the drinking water. There was no need to procreate at the time, because Adam and Eve were in immortal physical bodies at the time. Procreation of immortals would mean overpopulation is no time at all.
All of these blessings were rejected and then removes when Adam and Eve chose to disobey.