What qualia are made up of are not easy to be accurate about. My favourite thought experiment that interrogates this question is,
Of course it isn't. We have a very poor understanding of brain states. So all we can say is that Mary will learn something new today. But it's not reasonable to extend this to an assumption that a physicalist explanation of qualia is impossible in principle and will become available in the future.
As it happens I'm not a physicalist, and I suspect - but can't prove - that physicalism won't solve this problem.
But I also don't like poor arguments, and I think the Knowledge Argument is not a good one.
The problem is more fundamental. Qualia are definitively subjective and the only way to prove that physicalism explains them is to somehow make them objective - with some kind of qualia-ometer. Or consciousness-ometer. Or something similar.
That doesn't mean finding correlates - neural states, chemical processes, quantum uncertainty, whatever. It means being able to measure experience itself.
Without that you can build simulacra that show all the correlates, and possibly behave as if they're conscious.
But all you've done is built a robot. You can't prove it actually has experience - including self-awareness - unless you can measure experience with objective instrumentation.
This is a nice paradox, because it requires science to measure subjectivity itself.
It may or may not be possible. But clearly it's not possible now, and is unlikely to become possible any time soon.
We build things all the time based on the models of the universe we've got. Your argument strikes me as more or less saying, "sure, we built that jet engine, but unless we can measure what 'being a jet engine' is we've just not really built the complete, real thing."
If we build a thing that appears to have "experiences" indistinguishably from how humans appear to, then that is it. That is, the notion of "experience," as you describe it, is more or less meaningless in the context of the very physical world we occupy.