If God, Jesus, the devil, angels, and demons were all real, we still couldn’t rely on the Christian Bible as gospal (pun intended) — it was written by humans, specifically men, who could have misunderstood or invented things. Think of it like the Snyderverse in Man of Steel: Superman is portrayed as a brooding, violent character — but that’s not his true nature. In Batman v Superman, Batman is straight-up killing people — also not his normal characterization.
So even if much of the Bible reflects real events or real beings, parts of it could still be distorted, exaggerated, or entirely made up by the people who wrote it down.
Some gnostic Christian sects took their Zoroastrian roots a little more seriously than mainstream Christianity and argued that the God of the old testament is actually the demiurge.
The demiurge is an evil / misguided shadow of the true God caused by Sophia (the concept of pure wisdom) attempting to reproduce without the male half of her syzygy. As a result, the demiurge was created and dragged her out of heaven when he fell and tried to recreate heaven with the bits of her soul he still had. Humans on earth are just the little bits of Sophia’s soul tapped in the shadow of heaven that he made. Eventually they will reach gnosis (similar to the Buddhist Nirvana) and ascend back out of the kenoma (shadow heaven) and back into the pleroma (true heaven). Jesus (who was also the serpent in the garden of eden) is the male half of Sophia’s syzygy who came to earth for the second time to awaken the sparks of her soul so they can ascend.
I’m simplifying some things and smoothing the narrative to make sense since the reason Gnosticism never did as well as mainstream Christianity is the lack of a consistent narrative with which to create in-groups and out-groups to wage holy wars over, so the ones that did wiped them out. And for example I do consider myself gnostic but I mostly stay away from the metaphysical stuff other than in ways that they represent concepts important to a healthy life like mediation. I hope you enjoyed reading though!