Prefab house - yes or no?

So, the low heat storage capacity of the walls is even advertised by the prefabricated house factories.

But that has nothing to do with the heat transfer itself. And the storage capacity also depends on the materials used. It is complete nonsense to lump all manufacturers and construction methods together, regardless of whether they are solid or timber frame construction.

You can just open the window and ventilate.

The question is whether you want to walk through the whole house twice a day opening and closing windows. With three floors, I really wouldn't want to do that, especially if not all rooms are being used yet. The technology behind a ventilation system is very simple; the critical point is only the fans. It is a comfort feature, I agree with you. We also still open the windows from time to time, but I don't have to when the house is empty for 2-3 weeks.

One can surely open the window and air out

You can; but with highly energy-efficient houses (whether timber frame or solid) it’s not that easy anymore and also somewhat contradicts the energy concept.

First, the requirements for shock ventilation pose a problem for working people; not to mention during vacation times, and second, it’s also nonsense if you have such a house that you’ve sealed meticulously to let energy escape again by throwing open the windows.

Better to have a central controlled residential ventilation system with heat recovery. Comfort of the highest order.

Correct, that has proven itself with us as well. I wouldn’t build without controlled residential ventilation anymore. But you have to get used to keeping the windows closed first.

According to our general contractor, you should still ventilate the steam through the windows in the bathroom after a hot shower...
Or sometimes it’s also good to air out after intense knob vibrator orgies...

So, with the low storage capacity of the walls, prefab house factories even advertise. Scanhaus Marlow Marlow in the brochure: In winter heated up faster, in summer cools down better overnight. That can't be denied. That's how it is. Whoever wants that gets it. Whoever wants the other must build solidly.
Regarding building technology: What isn't there can't break. As little as possible. Gas boiler plus, but only because they force us to!, solar cell for hot water heating. That would be my advice. Control technology is vulnerable. All the systems for who-knows-what just please the heating specialist afterwards.
You can certainly open the window and ventilate.

I did say, in summer that can be an advantage...
It is also far from me to speak badly of prefab houses in general, both have their justification.
Ultimately, when you look at the end product "house," for me there are more pros with a solid house and more cons with a prefab house.
That is why I am asking for really tangible advantages, not during construction but of the end product house in prefab or timber frame construction.

According to our general contractor, you should still ventilate the steam through the windows in the bathroom after a hot shower... Or sometimes it also feels good to air out after intense knob vibrator orgies...

Why is that? When I shower, for example, the humidity in our place rises from about 25% to about 35%. What humidity should one still be "ventilating" out?

According to our general contractor, one should still ventilate the steam through the windows in the bathroom after a hot shower...

Every now and then we do that as well, but it is not often necessary. When someone has showered, the humidity rises to >80%, but it is back under 60% within 30 minutes and at normal levels (40-45%) after an hour. And that is also the next advantage of controlled residential ventilation (in this case with an enthalpy exchanger): You always have a good humidity level of 40-50% and not 30% and below, as is often the case in apartments in winter.