Preparations for central air conditioning in the new building

What problems are supposed to occur there?

A friend told me that he had problems with energy efficiency after installing an air conditioning system. Unfortunately, I don't know exactly what happened. And in some thread here recently, I also read that someone gave up KfW funding because of the air conditioning.

The developer had suggested that the preparations be taken into account accordingly during construction

Yes, that is the correct approach if you don’t install everything right away and immediately.

Now I first wanted to see what kind of preparations are even necessary.

For the "usual ones" I had already described that. Refrigerant lines and power/control cables from the location of the outdoor unit to the indoor units. At the indoor units condensate drain (sewer connection). Nothing more is needed in the cheapest variant.

the actual heat development observed over 1-2 summers. You never have the new building condition again.

It depends on where the house is located and how shaded it is, but one thing is certain: summers are getting warmer.