Yeah, I think you are right. "The content of consciousness" and "consciousness" are different things, and I mixed them up, when writing that sentence. I can watch the content, but not other parts that may be producing it.

Moreover, thinking about it, I come to a conclusion, that if I cannot reflect on qualia creation, then it is a (weak) evidence for qualia created by consciousness. I suppose the consciousness is harder to reflect on than other things, hard to map it into states of the content of consciousness. Like, I can reflect on my vision and see some hints on how I get these wonderful pictures, despite it being definitely not consciousness, I can reflect on how I produce or decode language. And to my mind it is because consciousness was devised to reflect on these things, so I could report on my observations to others. But to reflect on itself is a wholly different matter.

We can't even meaningfully prove that human beings have qualia

We can’t meaningfully deny humans have qualia, there would be too much baby and not enough bathwater.

I would not deny it. The reason people accept current evidence is, after all, because they can relate to the experience of qualia, even if there's no complete objective understanding of it yet.

We can't even meaningfully define the concept.