There is one more step that can be made, but you are right, there’s nothing further that can be said. That is, nothing about what God is, only what God is not. And black box falls into that category. If science had to first eliminate all what God is not, scientists, with their meticulous methods, could discard one thing after another until the very end of time and they may not arrive at that which remains after all things are discarded as not-God. Well, how can one convince them that we can know the unknowable? Maybe they should ask how is it possible that consciousness, no matter if emergent or as a primary constituent of the universe, is the same, without any attributes, in all human, but essentially all living, beings? Or maybe they should just try to imagine what if there never existed anything. Not even time and space. Or, better yet, how would it look like if existence itself was not.