I prefer the definition of Myth (Mythos) as the antonym of another Greek word, Logos.
They both can be translated as “word,” but “logos” is a word the truth of which is based on logic and experience, while “mythos” is a word or meaning which is based on tradition and authority. Some maybe most people consider science based on logos, while religion is based on mythos, However Jesus is designated the Logos in the Bible, and Jesus criticized the Pharisees for their tradition based faith, while calling on His followers to have a faith based on experiential knowledge and logic. Therefore Christianity rejects Mythos, ideas not based experience and logic, out of hand.
I would say that the Birth of Jesus and His death and Resurrections may be miracles, but they are not myths, They are based on the experience of those who witnessed them and the Church at large and the theology of the Church.
On the other hand the Virgin Birth is based on a misread prophecy taken out of context. It also leads to unchristian dualism. I would not say that the Virgin Birth is wrong, I would not say that it is very important either. It might be important as a sign, but it is not important as a fact. It is a sign that Jesus is the Messiah, but not the only sign and not an important sign.
That is why I reject survival of the fittest as the basis of evolutionary theory. It is a myth in that it has not been verified by experiment or carefully designed field observations. That makes it unscientific, which is a real scandal for a two hundred year old theory.
Just because it is not verified does make something untrue, but ecological natural selection has been verified many times and so it is about time we replace survival of the fittest with ecological natural selection.