Underfloor heating air-water heat pump. House too warm when the sun shines

I correct, the data should be in the documents/calculations from your energy consultant.

The house is a new building, 170 sqm with underfloor heating

For a standard Energy Saving Ordinance building with buffer, that will already be normal. Ours is return flow controlled, therefore not directly comparable. I believe it is 22°C return flow at 12°C (25-27°C supply) and 25 or 26°C return flow at -12°C (so around 30°C supply).

No, a Tecalor thz504 air-water heat pump (integrated unit with controlled residential ventilation and heat recovery)

Do you know anything about a Tecalor THD 400 AL?

I correct myself, the data should be included in the documents/calculations from your energy consultant.

It makes sense to do a room-by-room heating load calculation and design the underfloor heating based on that with the appropriate supply-return temperature. Then select the heat pump accordingly. Unfortunately, this is rarely done. Usually, a heating load per square meter for the entire house is assumed and applied to all rooms, regardless of how many exterior walls a room has. When the underfloor heating is then designed based on this, it doesn’t match in some rooms (mostly bathrooms). The heat pump is then selected by guesswork, often hopelessly oversized...
In the documents from our energy consultant, there was no room-by-room heating load calculation. The company commissioned by the heating installer also did not perform a room-by-room heating load calculation but assumed a flat heating demand per square meter. So, that meant doing it yourself or commissioning it externally.

It makes sense to perform a room-by-room heating load calculation

This apparently was not done.

We have -4 degrees at AT, 31 degrees supply temp. But we also need DS, otherwise it is too cold for us. That way we have 22.5 degrees in the house.