Perhaps the whole of philosophy originated from the attempt to understand how it is possible to know (epistemology) - it may be that the metaphysical schemes were driven by this question.
I think that the monist metaphysics of mainstream Christian philosophy is organized-around the intuition that reality must be 'inside' God or else God cannot know reality; and if God cannot know reality then neither can we - there can be no real knowledge.
(A God which is inside a pre-existent universe, from this perspective, can never know it - can 'only' have theories about it - and if God doesn't know the universe, he cannot master it... This is assuming that we insist on an omnipotent God, rather than a God which is 'merely' vastly, incomparably and incomprehensibly powerful.)
But this argument does not necessarily work, because all these things (metphysical descriptions) work by analogy - and 'even-if' the universe is inside God, then that is no reason - no reason whatsoever -why God should understand it, know it.
The fact that something is inside oneself does not make it more understandable than something being outside oneself. We do not understand our hearts and kidneys, we do not even know when a cancer is growing inside us - our insides might as well be outsides from the point of view of knowledge.
And this even applies to the brain and mind - the part of our mind which knows is a tiny part of the operations of the mind.
There is no way of imagining a situation in which knowing is natural, intrinsic, and self-validating.
To insist on this leads to nihilism.
The framing of the question renders it unanswerable - we can successfully critique and expose the flaws in another person's views, as monists successfully critique pluralists - but all possible articulated views are incoherent hence indefensible - and monism is itself incoherent hence indefensible!
My impression is that epistemology as a whole is a badly-framed question, a red herring, at the deepest level nonsense, a confusion, an artificial artefact of some kind.
So, if not - then what?
Human understanding necessarily is in the way of relationship narratives - stories.
And/ yet/ if you try to unpack, translate, summarize the stories - to capture them in non-stories and detach them from human relationships (detach them from motivation and purpose and choice) - then the incoherence of metaphysical questions comes flooding-back to suck you down towards nihilism!
Note added: The first and second commandments (to love God and neighbour) are about relationships; Scripture is full of people and stories; Jesus taught mostly by stories. Clearly relationships and stories are primary for Christians. If we can't comprehend (relate to) people, relationships and stories as primary; but must translate everything into impersonal, abstract (legalistic, philosophical) principles (laws, rules, regulations) then it is pretty difficult to be a Christian - because we will get Christianity at second hand and without the intrinsic power that comes from personal engagement. Often, and now, abstraction yields apostasy.