I think a point worth making is that everybody views god claims as something that must be proven with absolute certainty, but when it comes to other knowledge claims, degrees of certainty are accepted.

I say that absolute certainty does not exist since all knowledge is tentative. And with that being true, I can say that I know a specific god does not exist, because I say so with a relative degree of certainty based on my knowledge of how that definition of a god came to be from a historical or psychological lens. Whether or not I am a gnostic atheist depends on the definition of the god being presented. A generic, "invisible" god which exists entirely separate from our reality is not a god I would claim does not exist. But any god with further defined characteristics, scriptures that supposedly pertain to it, and so forth, I claim I know does not exist for the reasons above, with the understanding that all knowledge is tentative and subject to change given new information.