Rental apartment - Uncertainty about installed decentralized ventilation systems

The house is a low-energy house with triple-glazed windows. Installing ventilation systems there that (uncontrolled) let cold air into the apartment in winter somehow doesn’t fit at all.

Why shouldn’t that fit? You can still do window ventilation today and you also don’t have heat recovery there. The entire concept must have been calculated by an energy consultant. If one point isn’t so good, then you can compensate for it elsewhere with additional measures.

Installing ventilations there that let (uncontrolled) cold air into the apartment in winter somehow doesn’t fit at all.

I fully agree with What doesn’t fit? Of course, there are proponents of controlled residential ventilation with or without heat recovery in a house. I am also a fan and have one myself in my single-family house. But there are also many builders who do it differently, possibly dispensing with a central ventilation system. Whether it makes sense or not is not to be discussed here. One has the philosophy, the other their own truth. A ventilation system is meant to ventilate so that nothing molds. They are all “low-energy houses,” the term says nothing. But if I invest in a condominium to rent it out, I weigh comfort against costs. What is necessary, what is optional, where can I save. I think you are expecting too much there. I can also imagine that you misunderstand or perhaps overestimate heat recovery. It is not a heating replacement.