Well, yes, and believers have long treated God as a real entity without apparently noticing [he] never appears, says or does and has no description appropriate for a real entity. Even the unicorn is better off than God in that regard.
No one cares what believers believe. That is their own business. This discussion is about theism, not what some believers believe. You asked me to explain "God" in a theism context. That's what I'm doing. And it has nothing to do with anyone's belief. It has to do with the profoundly unknown, and our human fear of the unknown, and how most humans choose to negotiate with the unknown so as to deal with their fear of it. That's theism. That's what the God ideal is about, and for. And it's a cognitive phenomenon, not a "thing".
But God exists, and gods and other supernatural beings exist, solely as concepts / things imagined in individual brains.
They exist as much more then that. They are part of a universal human cognitive phenomenon. And please keep in mind that this phenomenon is just as grounded is human physicality as every other human cognitive phenomena is. We cognate God the same way we cognate infinity, or perfection, or randomocity, or luck. These are all cognitive meta-ideas that we use to develop and evaluate our other ideas of existence. They are not "things". They are cognitive phenomena. So please stop asking for evidence of their "thing-ness". There is none, because these kinds of cognitive meta-ideas aren't things.
Search the world external to the self and there's no trace of them.
There is no "world external to the self". That is a delusion peddled by philosophical materialism. Apart from cognition, there is no "world". There is no "self". There is no God. There is no anything. "I think, therefor I am." "I don't think, therefor ... nothing."
No gods existing in nothingness is of no consequence, whatever. Yet for some reason you keep asserting this as if it's of the utmost importance. When it can't possibly be of any import at all.
Otherwise atheists would have nowhere to stand, and religion wouldn't be losing its fans in the First World.
Atheists and religion have nothing to do with theism.
The world would be a dull place without mysteries. But at least from my point of view, we work to solve mysteries in order to understand them, whether they be local and personal, or those of world-class stage magicians, or about the nature and origin of the cosmos; and we only take pleasure in the sensation of being mystified (on those occasions when we might do so) while we're on our way to seeking to solve them.
Solving mysteries regarding physical interactions is all well and good, but it's not really solving the great and profound mystery of existence, and of our being a part of it. Nor will it ever. And if you think it will, you have fallen into the delusion of scientism.