There’s no mention of a ton of very significant things we now know to be real in any holy book. Why isn’t that stuff enough “proof” they’re “fake”?
I also reject your out-of-hand assertion that whatever one thinks about the world's existence has the same meaning to someone as your mythical being has to you.
How blown would your mind be if I posited to you that what you call "GOD" is the universe? Your holly book says he is everywhere and everything all at once, does it not? That "He is within all of us", and yet we are the universe observing itself. He came about out of nowhere with no trace of origin? We don't know what caused the big bang, it just happened.
If aliens exist, it's because the universe "allowed" it to happen (aka the statistical probability is high enough for it to occur or we would not be alive having this conversation) not some conscious divine being.
Still labeling pre Big Bang as SpaceTimeTime or calling that Space Time and relabeling what we experience as local space time doesn’t really matter here. The point is our Big Bang could be happening infinite times in a multiverse without beginning or end. That’s one possibility where there isn’t anything conscious to point to as a GOD just the same kind of things which make up physical reality.