Or it could be an accurate description of a God beyond existence as we understand it.
"Beyond existence" is not something that has been established as being a real thing. And, until such a time as it is shown to be possible that something can exist "beyond existence" - there's no good reason to believe any such claims. Once again, I could just as easily put flying unicorns in the category of "beyond existence". But it still wouldn't mean anyone was justified in believing they're actually real.
You also don't seem to understand that negative theology is a thought experiment. It's not an actual way of describing things. Because we can only explain things in relation to other things. If you don't know what a ship is I might say it's a large boat. If you don't know what a boat is then I would have to explain it in reference to a vessel that floats on water, etc - until I get to something you have experience with or you already understand and then I can explain a ship in reference to that. But we can't explain things solely on what it isn't. If I say there I have a device that's not a computer and it's not alive and it doesn't have any minerals in it - could you then understand what that device is?
"Beyond existence" is just an Ad Hoc response you made up to try and rescue a failed hypothesis. There's a huge difference between following the evidence where it leads vs making up new terms so you can try and lead the evidence where you want it to go.