Foggy windows despite ventilation system

Regardless of how well or poorly the ventilation system works, the windows must not fog up like that. The windows are soaking wet, with an average of 30% humidity and 18-19°C... not acceptable.

Okay - what can I do? Have the windows checked again?

Sometimes measure the surface temperature of the glass with a suitable thermometer. Theoretically, at 35% rel.LF and 19°C, dew water should precipitate somewhere at 4-5°C. However, the windows should rather have 15-16°C. Your damage pattern can actually only occur with intact double-glazed windows and about 65% rel.LF.

When you look at the values, I cannot imagine that the ventilation system is operating correctly. In the end, there is no improvement in the room air at all; it only becomes acceptable again when the windows are opened. I would rather address this here.

Is this double glazing?

When you look at the values, I cannot imagine that the ventilation system is running correctly. In the end, there is no improvement in the indoor air quality; only when the windows are opened does it become acceptable again. I would address this point first.

Is this double glazing?

Thank you for your message. Yes, the panes are double glazed.

Wenn man die Werte sieht kann ich mir nicht vorstellen dass die Lüftungsanlage korrekt läuft.

But you cannot conclude that from the values.
The development of the CO2 concentration is quite normal for a standard single-family house controlled residential ventilation system. It would be too high for me as well, but it has nothing to do with the problems.

The system should have ventilated much more by now, especially in auto mode. The values rather suggest that no ventilation system is in use at all, right?