I used a 2017 Kickr for years then switched to a borrowed Tacx Neo. The Neo was massively quieter, most of the noise is from the drivetrain of the bike itself. I gather the 2018 Kickrs onwards are similar. Using a decent foam mat will also reduce vibration / noise transmission to the floor of the room. But the Neo is about as quiet as it gets, given that you need a chain / cassette / ring.
I guess that a belt drive would be quieter and possibly one of the virtual shifting bikes with what’s effectively a mechanical singlespeed set-up, but moving parts are always going to make a noise. The pre 2018 Kickr uses a toothed belt to drive the main flywheel, which is where most of that noise is from. Wheel-on trainers, from past experience, are really noisy and also create vibration at the same time.
Anyway, the Neo is great in terms of noise – few moving bits – and function, but also quite expensive, though they are user serviceable – unlike the Kickr, which is actively user hostile if the bearings wear out – so a used version might be a reasonable call.