Construction costs are currently skyrocketing

Could it possibly have been about passive house owners who thought a passive house warms itself?

Then we have a part-time passive house, from April to October.

Of course, you are absolutely right. But if no one is there, no "waste heat" can be generated either.
Wasn't it about 100 watts per person? And hot water is overrated too – right?

That is one of the reasons why passive houses, by strict definition, have not become widespread. Solar gains are nice and all, but they can fail for a week at a time. The incandescent bulbs of my youth with their corresponding heating output have been replaced by energy-saving LEDs, and unfortunately, now the 200W of waste heat in the living room is missing. And instead of a housewife and breadwinner, nowadays often both parents work, and the children are at school until the afternoon. The entire energy balance is now different, and the newly added access point no longer compensates for it.

Well, in the narrower sense (so when we talk about a Feist passive house), I believe the idea was to insulate thickly and do heat recovery with the ventilation system. And then the remaining heat demand (after calculation and simulation of passive heat gains from people, the sun, and household appliances) should only be very small (please look up the exact numbers yourself). And because that is so little, heating is done through the ventilation system, which you have anyway. The heat absorption capacity of the air is limited by the temperature at which dust begins to smolder, and the airflow should not be increased for heating purposes. So really only a little heating will be added to the airflow that is already necessary for hygiene reasons (of course depending on the number of people in the house).

Then you can save on other heating systems (except maybe electric underfloor heating in tiled areas, especially the bathroom for comfort). I haven’t heard of anyone building an EH40 with such minimal heating. Is a fully comprehensive air heat pump with water underfloor heating so affordable that people prefer to forgo the extra energy consultant costs for the PHPP and a few extra measures for insulation for a higher building standard (serious question)? Or is the additional cost simply too high? Or is there so little trust in science and energy consultants (maybe with good reason) that this can work? I mean, these things have been around for a while...

It seems more sensible to me to invest in a higher quality building envelope than in a higher quality heating system that will eventually break down.

Solar gains are nice and all, but they can also fail for a week. The incandescent bulbs of my youth with their corresponding heating output have been replaced by energy-saving LEDs; unfortunately, now the 200W of waste heat in the living room is missing.

Yes, what really makes me suspicious is the tendency to heat directly electrically (infrared, electric underfloor heating, partly also water flow heaters; because: you need so little anyway and that comes from the photovoltaic system) and the devices for direct electric heating are so cheap anyway that you can heat a lot before a full heat pump would pay off.

But if I now only have to provide a little supplementary heating with a maximum efficiency of 1 direct electric heat, couldn't I also provide much more supplementary heating with an efficiency of 1:3 using an air-to-water heat pump and only consume the same amount of electricity?

Actually, a passive house is defined in such a way that it does not require a dedicated heating system and stays warm through the recovery of waste heat. Additional heating is used at most on the few coldest days of the year. In this respect, you might have a building envelope at passive house standard, but strictly speaking not a passive house.

A nice definition (regardless of the technical specifications):
“A passive house is a building in which heating and cooling have such a low energy demand that it can be provided with very little effort and at the same time the energy demand for all consumers in the building is so low that it can be sustainably covered by a renewable energy supply.”

Whereas a 150sqm house may still have a heat demand of 2,250 kWh per year. This is not negligible and is often (mostly) not manageable by controlled residential ventilation alone. So, a heat pump is added - preferably an air-to-air heat pump, which can then cost a lot of money in deep winter if planned incorrectly (see Proxon).

Then you can save on other heating systems (except maybe electric underfloor heating in tiled areas, especially the bathroom for comfort). I haven't heard of anyone building an EH40 with such minimal heating.

Sure, that is offered and installed very often. Bien-Zenker offers it as standard for their 40-series houses. Comfort climate heating. So air-to-air heat pump. Streif Haus as well. There are various providers that rely on this.