Air-to-water heat pump new build - single-family house with basement - model?

It says there: COMMON control! That means both devices must be able to be operated via a common control unit.

Exactly, that's why the question whether this is any "good" or if certain models can be recommended here.

The joint control does not necessarily mean, however, that the devices must also come from one manufacturer.

There only has to be a joint control X. However, this can then control devices from manufacturers A, B, and C.

I have here from my heating technician an offer for Vaillant Arotherm plus and recoVAIR ventilation system, because the two can "talk" to each other via their own BUS. Otherwise, according to his statement, a KNX system would be necessary, which deterred me due to the initial costs. I don't know if the statement is true and I have not yet decided.

No, there are more possibilities than KNX. It is certainly significantly easier with it, but there are also more simple and proprietary solutions, especially in HVAC.

If you don't want or can't read up extensively and deal with it then:

Take both from a manufacturer that offers a [Bafa] capable control system.

Take a modulating heat pump with low minimum output and maximum output matching the heating load.

Take what the heating engineer you trust installs.

MUCH MORE IMPORTANT lay out the underfloor heating correctly.

If you don’t want or can’t read up extensively and deal with it then:

Take both from a manufacturer who offers a Bafa eligible control system.

Take a modulating heat pump with low minimum output and maximum output matching the heating load.

Take what the heating engineer you trust installs.

MUCH MORE IMPORTANT lay out the underfloor heating correctly.

If you don’t want or can’t read up extensively and deal with it then:

Take both from a manufacturer who offers a Bafa eligible control system.

Take a modulating heat pump with low minimum output and maximum output matching the heating load.

Take what the heating engineer you trust installs.

MUCH MORE IMPORTANT lay out the underfloor heating correctly.

As so often, I find it hard to trust anyone, because just from a few construction companies and heating companies I get very different statements...

Basically, almost every company offers me the Viessmann Vitocal 200-S. After consulting with various heating companies, almost all of them are not satisfied with Viessmann and recommend Weishaupt or Stiebel Eltron. One recommends indoor installation, another says that the split heat pump is best, bla bla bla...

It’s similar to the ventilation system... There are so many pros and cons to every type that it’s slowly becoming really disgusting to deal with.