The fundamental problem isn’t whether God is real (ie, the “Higgs particle” of particle physics) or what God is (ie, the “true tree of life” of cladistics), but that there isn’t any God. Posing these questions thus moves things ahead.
The fundamental problem is instead: why isn’t there any God.
The solution of this problem is the answer that if God (ie, belief) would have been real, then the old lady should have shot the bear with the broom handle. There is simply an unsurmountable aisle between reality and belief, and whereas reality is given as factual, belief is just as given as non-factual. Never can the two meet.
The fundamental problem is thus understandable, but insoluble (per definition). It is actually the most fundamental among those problems that are insoluble. Not everything is thus possible.