As for what the mind might be if it is not the brain, that is not a short discussion. As a pointer, take a look at various substance or property dualist views, or monist views such as that of George Berkeley.
We have no external experience so we have no way to truly know the answer.
Could the brain be a conduit for some external interface for each mind?
Could the brain be an interface for some larger shared mind?
Could the brain be a vessel that carries the mind while the brain is alive?
Could the brain be a figment of the mind?
Just because science can't yet describe subjective post-death experiences doesn't mean they don't occur.
That being said, I'm personally in the rational constructivist camp wherein I think that our mental "scaffolding" obscures our ability to be objective when we try to reason about this. Though I am hopeful we find some answers someday!
You wrote a rather lengthy post saying you disagree, mixed with an empty appeal to authority, but you provided no counterpoint or evidence or rationale or hypothesis refuting or contradicting the assertion that the mind is the brain.
If the mind is not the brain then what is it, then?