Blanket strong agnosticism is the view that it is impossible to know whether or not there are any supernatural beings.
Since it is impossible to observe supernatural beings directly, we can only infer their existence as the best explanation for some observation or other.
The trouble is that none of the explanations are testable.
To be testable means that it is possible to predict observations that the original hypothesis was not designed to explain. But the only relevant observations with this kind of “argument” are always just the observations that they purportedly explain.
They all amount to a declaration that such and such is the case because there is a supernatural being with the desire and ability to bring it about that such and such is the case.
They could as well “prove” the opposite. Suppose that such and such were not the case. You could then “argue” that such and such was not the case because there was a supernatural being with the desire and ability to prevent it from being the case.
Supernatural “explanations” are always vacuous verbal formulas.