If God made everything good and thus the garden of Eden was “good,” why was Satan there to tempt Adam and Eve?
At least one thing was not “good” in the garden.
Genesis 2:18 The Lord God said, “It is not good for the man to be alone. I will make a companion for him who corresponds to him.” Loneliness and companionship existed before Adam got a companion.
A thing cannot exist without its lack also being possible. Electrons exist because a lack of electrons is possible. There is gravity and anti-gravity. When there is only dark, light may not be present, but it has potential. When there is no possibility of evil, good does not exist. Satan is lurking in the garden because obedience, freedom, righteousness, etc. are present.