To me, the hard problem of consciousness is the link between observable physical activity of matter in the brain, and conscious experience. Science has found correlations between brain activity and experiences. But nothing is known about a mechanism of cause and effect which connects them.

Dualism is probably mistaken. The only evidence we have for anything about physical reality comes from experiences. It does not seem logical to believe that there is a physical reality which is separate from conscious experience. Quantum theory hints at this, with how the observer becomes significant. But this does not make understanding how it all works much easier.