Electric window opening as an alternative to a ventilation system?

Not entirely convinced, otherwise I wouldn’t have contacted you here. Of course, I also have concerns about the system, no question. But less about the inflow of cold air, and more about whether the amount of air exchange is sufficient as well as the durability of the electric drive of the windows.

I would also be interested to know whether such ventilation systems also prevent humidity when it is muggy outside?

Do you have these anti-hum humming blinds on all the windows?

We have equipped all the bedrooms with fly screen blinds. Additionally, the bathroom, shower room, and kitchen. In the living room, we will have a fly screen door installed at the terrace door. The other windows in the living room and other rooms are not equipped with them (as far as I haven't overlooked a window). Although I now realize while reading that we should have installed one more in the living room. We can't just open the terrace door at night – risk of burglary. That was not thought through enough.

Now a different question. When it is muggy outside, the ventilation system also draws in the moist air, right? It is then pulled out at another point. A cycle.

Good question – I think then we will limit the system operation (for half a day or so) until the high humidity outside decreases again.

If you turn off the system at night and ventilate with the window, then you can also ventilate all day with the windows

Well – two points about that: First, we are not at home during the day, so regular ventilation only through the windows is not possible (leaving aside your suggested system, since I have not looked into it). Second, it is considerably warmer outside than inside during summer. So it would be like now (without a ventilation system in the apartment): during the day, we currently keep the windows closed and try to keep the heat out as much as possible. At night we open the windows to let the cool air in.
We will probably operate the fans at 25% during the day during extreme heat (when no one is at home) and then switch to shock ventilation in the evening (unless we open the windows). Afterwards, we will continue running at 50%. This also ensures reasonable air exchange. This is how I currently imagine it. Whether it proves effective in practice remains to be seen.

I would also be interested to know if such ventilation systems also keep out the humidity when it is muggy outside?

No, unfortunately that does not work. As far as I know, you still need an air conditioner for that or must shut down the system manually or via an outdoor air sensor when humidity is high.

I just think that with this system you will eventually spend significantly more money on heating energy than you save now on installation...

...but whether the amount of air exchange is sufficient...

If, as described in the video, the heat is supposed to remain in the building envelope with this system and the window frame does not have built-in heat recovery, then certainly not.

We are also curious and looking forward to our decentralized system. Probably we will still open the windows at night from time to time during the summer and turn off the system.

As far as I know, you should never do that. If there is a ventilation system, it has to run 24/7 throughout the year. In the exhaust duct, there is a lot more than just fat residues. They are pure bacteria and mold breeding grounds. See here and the next few minutes:

[MEDIA=YouTube]AWD0HeZLufM[/MEDIA]

This is not so bad per se, since it is the exhaust duct. Wastewater pipes don’t look good either. Due to the constant airflow, it is ensured that all the dirt definitely does not enter the house. If you turn off the system, these microorganisms can find their natural way outside again.

[MEDIA=YouTube]AWD0HeZLufM[/MEDIA]

That is also where the problems come from in winter, when the humidity sometimes drops to 10-20% for some people. Turning it off is simply not an option.

Edit: Too bad, I couldn’t post the exact timestamps somehow. So: 39:15 and 36:45

Interesting.
However, you probably overlooked that WE have a decentralized ventilation system with heat recovery. The fan draws in outside air for 75 seconds, then rotates and blows out the inside air for 75 seconds. The air itself passes through a "heat storage stone." The units have wall thickness – there are no ventilation ducts in the decentralized system.
Some people find it an unattractive disadvantage that several fans are installed in the house – this would be a potential (visual) disadvantage.