Heat pump produces more heat at colder temperatures

Isn't that a misconception and exactly the problem why 95% of households have incorrect settings or heat inefficiently? ;)

I don't know, maybe we belong to the other 5%?
We no longer live there, but in the second year in that house, heating, hot water, and ventilation cost about €53/month.
I always found the settings perfectly adjusted and can't imagine that it was inefficient, just judging by the price.

Don't know, maybe we belong to the other 5?
We no longer live there, but in the second year in that house we had about €53/month for heating, hot water, and ventilation.
I always found the settings spot on and can't imagine that it was inefficient, now judging solely by the price.

That may be that it was satisfactory and "accidentally" fit for you and that you could count yourselves among the lucky "minority."
However, in my understanding, it is exactly wrong at this point to refer only to the "heating specialist" and advise against "fiddling around" yourself. After all, the heating guy neither knows the house nor the individual temperature preferences and can therefore almost always only make generic standard settings so that they roughly fit somehow. If at all!
Ultimately, it is always necessary in a new building to at least roughly familiarize oneself with the topic, to observe, and to make individual adjustments. Here we are not even talking about hydraulic balancing or similar yet. :)

That is probably correct. It definitely took me about two entire heating seasons until I had the heating there adjusted so that it also consumed little according to our living style (around €60 for heating + hot water).

The "heating specialist" of course roughly adjusted the heating and even performed a calculated hydraulic balancing. However, the consumption was still about 30% higher than after I took over.

In the case of the OP, we already clarified it over the weekend. The heating curve does not match the house.