We can postulate both naturalistic and supernatural theistic answers to what came before the big bang, but doing so is guesswork where your guess is as good as mine.

We cannot see beyond the CMB, which formed 380,000 years after the Big Bang. We can draw theoretical inferences back to the Planck Time. Our current technology is unable to explore before that, so the honest answer to your question is I don't know. It appears to be unknowable at present.

In the essay, I explored a naturalistic explanation consistent with the 1st law of thermodynamics, which says that energy can neither be created or destroyed. I felt it was fair for me to make a SWAG since theists the world over in uncountable faiths have made their supernatural wild-ass guess that their particular god created everything ex nihilo. To be fair, I have no idea whether the laws of thermodynamics were the same before the Big Bang as they are here and now; my intent was not to claim knowledge of what happened in the beginning. I suspect there was no beginning; My intent was simply to show that there are explanations other than "A magic man in the sky did it." when nobody has demonstrated that magic is a thing.