Again, what does that matter in the realm of the metaphysical?

Oh and aren't you making assumptions based of the physical observances that may have nothing to do with the actuality? Observable phenomenon only tells us what we see but doesn't always explain the why and how. Just because we are unaware of something that is not "observable" doesn't automatically negate the possibility of it's existence or even throw doubt on said existence.
It matters in the discussion of philosophy, and what it's reasonable to assume as truth.
If dualism doesn't meet the burden of proof, it's unreasonable to assume as true but is a mere matter of faith. That's just coherent rationalism. That's why positive claims are those that harbor the burden of proof, agnosticism of a topic is the starting disposition. You're adding on more assumptions, getting farther away from dualism in your above post by implying that it's not falsifiable, which would be another argument against considering it the truth.
Claims that are not falsifiable are not provable, and can be dismissed on account of that.
I'm claiming dualism lies within the realm of the metaphysical which means it can't be substantiated or un-substantiated so I've added no assumptions. I'm simply stating that the belief in the existence of dualism and the belief that dualism doesn't exist are simply that, beliefs that no physical science or philosophical logic can prove, dis-prove, take away from or add too.
Now if ever definitive proof/evidence that can be directly linked then the subject moves from the metaphysical into the realm of the physical, current neuroscience observations have drawn a
possible correlation but nothing more.
For all intent an purposes the subject is a moot point.
The subject is "can dualism be rationally justified."
It's not "dualism is a false belief."
So far, you seem to be saying no - it cannot be rationally justified.
We agree. Agnosticism on dualism seems the most rational approach.
Neuroscience does proffer evidence in one direction, and that's because
theistic dualism posits the mind as the body-less spirit that moves on when your physical body dies. Anything that correlates our thoughts, intentions and beliefs with the material world does run counter to that because it adds physical states as an essential property of the mind which counters the theistic dualists' view.
Gut bacteria alter intentional states(beliefs). Hormones alter intentional states(beliefs). This is evidence against theistic dualism, short of re-defining it which is special pleading.