Renovating beam layers ceiling/floor - Problems and questions

That will not solve your impact sound problem. Weight is king.

Yes and no. As the OP describes it, the disturbing noise here does not primarily come from vibration but from resonance. In this respect, the idea of sound damping is not wrong at all.

But basically, I agree with the strategy to address the issue above the joist level. This would at the same time offer the opportunity to use the joists purely for design purposes on the underside of the ceiling.

Yes and no. As the OP describes it, the disturbing noise here does not primarily come from vibration, but from resonance. In this respect, the idea of soundproofing here is not wrong at all.

Impact noise always arises from vibration excitation. The main transmission path here is through the beam, not the air path through the infill; if anything, flank transmission may even play a greater role here than the transmission path through the infill. Impact noise rumble occurs around 100 Hz and below. Cavity damping with glass/rock wool simply does not help at these frequency ranges.

Impact noise always arises from a vibrational excitation.

And in the guitar, the plucked string is at the origin, yet the resonator body is still significant.

Impact noise drumming occurs around 100 Hz and below. Cavity damping with glass/stone wool simply does not provide anything in these frequency ranges.

Bass reflex speakers may be out of fashion, but damping does have an effect there.