Sound insulation - differences in interior doors?

Standard doors would then be made of hollow chipboard core (no web)

Why not solid from the carpenter? There's not much difference in price (if any).

Solid wood is not recommended. The doors are usually quite heavy. In terms of price, you're looking at about a thousand each per door.

Price-wise, you're then also about a thousand per door.

???
Including the frame at around 500€ for spruce white as a basic option. "Better" wood is then somewhat more expensive, but that's a matter of taste.

In the last house, I had solid wood doors (they weren't heavier to handle, though, with Tektus concealed fittings) and now in the apartment, hollow core.

My main concern is the floor seal. Do you think an RSPK door with Schallex floor seal is sufficient?

Phew, for 500 euros you definitely won't get a carpenter door in the [Süden].

Then just order online and install it yourself. Even if you have two somewhat left hands, it will still work.