Oh believe me, I know Mary is not the mother of God. God is self-existent. God had no beginning and will have no end. God is the Creator. Mary is the created. However, Catholics constantly refer to her as the mother of God. Such as in the “Hail Mary”. “holy Mary mother of God, pray for us sinners, now and at the hour of our death, amen.
All of this is true, and no Catholic should dispute any part of it. The Church certainly doesn't.
But to deny the title "Mother of God" to Mary can only mean (a) Jesus is not truly God; or (b) Mary is not really Jesus' mother. Either one is Christological heresy, which no orthodox Christian can accept.