We go over this pretty frequently (like, four or five threads at least int he last month I believe) in Apologetics. Have you searched that forum? I’m sure you’ll find good references there.
Long story short, almost all the stories that some people have promoted as “the same as the Gospel but earlier” are one of three things:
made up or hugely exaggerated and twisted out of all recognition by pop authors with an axe to grind,
pretty universal themes (food, motherhood, travel, danger etc.) it’s almost impossible to find a real or fictional biography lacking, since these elements appear in most lives, or,
AD appropriations from a Christian community into a pagan one, distortions of Christian belief by relatively isolated groups, and/or assimilations of BC Jewish Messianic prophecies into cultures that had contact with the Jewish people for long periods.
One example of the first phenomenon is that many copycattists say Isis was a virgin mother, becoming pregnant with Horus after her husband died. Well, in the Egyptian story, Osiris, being a god, could never really die and was never eally alive in this world either, but the murder of Osiris by Set made the former less mobile and too weak to call for help or speak. His biology worked though, and Isis enabled him to impregnate her in the natural fashion with a little mechanical help (don’t mean to be graphic but it makes all the difference to the meaning of the story).
Another chestnut is that Mithra was born of a virgin. The Persians actually thought he had emerged full-grown from a rock, which was never a person at all, always a plain old rock.