I think you would have to be schizophrenic and suffer confirmation bias to believe in a god of your own creation. For me, a major stepping stone towards Atheism, was when I wrote a story about a hero, who became more powerful as I kept writing due to “power creep.” Did you know that in the beginning Superman could only lift cars and jump high and far, but later he could lift skyscrapers, and had the ability to fly? Well, my chunibyou capeshit character became OP too. (You know, the way Yahweh probably started as a sky God and then became the lord of everything on Earth.)
Gradually I started comparing my character to Yahweh, realized to my shock that I would rather worship my character than the capricious God who indirectly murdered everyone in the Book of Job. At least my character was charismatic, sexy, humane, and had a more consistent moral compass. If I had to choose to worship a God without evidence, I’d choose the one I had designed myself.
Someday I would like to know how many Sci-fi/Fantasy authors deconverted largely due to writing? I haven’t read of anyone else doing so.
Anyway, the possible interpretations multiplied in my writing in the way theology develops – I realized I had created a theology with a pantheon of “Gods.” I had to introduce a villain as an antagonist, and he promptly became like Satan – a mechanism for explaining why my hero didn’t have the power to fix everything, and why there were problems in the world. (Unlike Satan, he had good intentions though, so I guess my story was more sophisticated than the bible.)
I began to suspect the bible was little more than a collection of highly-polished fan-fictions based on some ancient folklore. That’s how my research into religion began. Sometimes I wonder if I wouldn’t have figured out it was BS if I hadn’t written the story. Supposing I had been a wage slave after High School, with less hours for thinking about my writing? (It’s not a comforting thought, and another reason I don’t like low minimum wages. Surely that increases the religiosity in the poorer countries….)
You don’t have to be a writer to read enough and come to the same conclusions though. A study showed that the whether a child was brought up with religion makes it easier or harder for them to tell if a story is fictional.