Even in Genesis, the Earth was influence by angels (bene Elohim--בני האלהים) as well as demons.
It has absolutely nothing to do with the Oneness of God.
I don’t read the Bible literally in every respect. I think a lot of it is symbolical, allegorical, &c. I don’t believe that God ‘made the world in seven days’, or the snake-in-the-garden story, for instance.
And I don’t believe in demons, beyond their existence in human imagination - which can become very ‘real’ in effect, if you dwell upon the idea ‘religiously’.