Many Eastern religions make this claim about God. So do Muslims. Unfortunately it is incoherent.

To say God is unknowable is either a statement about God, or a statement about ourselves. If it is a statement about God it is an affirmation that he has no properties capable of being known. And yet having at least one property is what differentiates existence from non-existence. If God has no properties, then he doesn’t exist. If it is a statement about ourselves—our ability to know a God with specific properties—then it is self-refuting because the statement itself is a claim to know something about God: he is unknowable. If God was unknowable, we would not even be able to know that He was unknowable. This can be pointed out by asking, “How do you know God is unknowable if nothing can be known of God? Isn’t that something you know about him?”

Either way you look at it, that statement is incoherent.
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