I don't think you've thought through what you're trying to assert. A god could make you believe anything they wanted to about the earth. So if you cannot disprove a god, then you cannot disprove the theory that the earth is flat.
(a) "I can prove earth is not flat" (using this methodology) (b) I cannot prove there is no God, though I may believe the prevalence of evidence does not support the hypothesis, there's no scientific test that I can design.
I can disprove that the Earth is flat with the incredibly varied, concrete, observable evidence that it is not. It comes in many forms and is undeniable, hence the lengths flat earthers have to go to to “prove” the evidence is all just a collection of lies that serve some nebulous, nefarious purpose (they don’t even agree on what that is) that serves some faceless evil group they prop up (usually “the deep state” or Jewish people). On the other hand, I do not have concrete, observable evidence that God does not exist. That’s the thrust of my point.
Perhaps you might think this is bullshit because *obviously* this world is real and not an illusion and there is *obviously* no evil demon to deceive us into thinking the Earth is spherical instead of flat.
And yes this is what philosophers do. Nobody here is arguing that such demon exists and is actually deceiving us, but since you've accepted you can't prove god doesn't exist (maybe mis-step for you since you're probably not the philosopher type), well, can you prove such demon doesn't exist? Seems to me the same thing.
This is essentially Descartes evil demon issue. If you can't disprove that an evil demon (with god-level powers) is deceiving you at everything you perceive, then how are you going to be sure about anything? (including that the Earth is not flat?)
It has always been a difficult philosophical issue about how much we can trust reality itself.