Plan the ventilation system before the structural shell construction begins.

Duplex house is spelled with two p's like Paula.

and what does that have to do with the thread?

Mechanically, it's about a semi-detached house, which we would then simply call a semi-detached building.

Are there decentralized ventilation systems that are actually unproblematic (quiet), preferably lasting a lifetime?

I would listen to various decentralized devices live, as there are significant differences that cannot be seen on paper, for example in the starting behavior. For not too many rooms, I would also prefer decentralized units per unit and record the operation in the rental agreement. In owner-occupied single-family houses, rather central systems.