Panasonic Aquarea heat pump design for two buildings

You are right. Unfortunately, I haven't had much luck in Goren yet. Maybe my questions were also too specific.

You definitely have a request with your wish to also heat the garage that does not meet the standard. And, although there are one or two experts here, mainly private builders are active here who do not have such a special situation themselves and therefore can offer little help.

Recommendation: Separate systems for separate tasks.
Task heating: Living spaces at living room temperature (20° according to DIN).
Task frost protection monitor: Keep certain enclosed rooms that lie outside a thermal envelope with living spaces frost-free (>=5°C).

There are specially designed devices for this purpose. Unfortunately, to my knowledge, mainly based on the principle of direct heating. However, this should actually not be a problem, since maintaining 5° is not that difficult (in our latitudes).
Possibly, as already suggested (I think in another thread) monoblock air conditioning. It can probably heat with a coefficient of performance of 1:2.5-3.
But I am not sure whether they still operate so efficiently at such low temperatures or whether the thermostat is that accurate in this range.

Sorry, but… It’s already absurd to retrofit the heating system in a new house after 8 years. Presumably, back then it was only "planned" based on forum inquiries. Heat pumps have been "IN" for over 10 years now.

Who actually does laundry in the garage? Ok, there seems to be a lot of space there to hang laundry to dry. But you need additional energy for the garage. And if no clothesline is used because a dryer is in use, I wonder even more why that unit is in the garage.

No matter what we write here, you need a professional who assesses the current situation and shows possible options. Who planned this strange setup "back then"? Is the "Heizi" (heating technician) still around? He would be my first point of contact.

The investment of surely 10-15k€ would have to be "heated back" first, despite (I read Photovoltaic and storage?) partly "free" energy.

With all the existing components and installation, it is relatively complex for a (cheap) solution.