Very wet windows overnight

I would basically want to know how old the building is, what kind of windows they are, which room it is, and whether the building has possibly been renovated. Maybe one does not fit the other? I don't see a photo/video here. You should actually write more about the flow temperature or take photos of the existing system. You can't just assume here that it's due to insufficient ventilation if ventilation is taking place. What is the temperature in the room? Is it heated?

The OP wrote something about 60-80%, that is just way too much.

The OP wrote something about 60-80%, which is simply way too much.

This morning I probably would have had it too, but only after airing out. In autumn, the humidity outside is simply higher. You also can't get rid of the moisture because the humidity outside is higher than inside.
If you then have cold windows because they are drafty or single-glazed, it is clear that the moisture primarily condenses on the windows.

Where are the damp towels dried afterwards and where is the rest of the laundry dried? If in the apartment, can the laundry possibly be dried elsewhere?
Alternatively, get a dryer.

Where are the wet towels dried afterwards and where is the rest of the laundry dried?

THAT is the most important question. If the windows are drafty, the indoor humidity should rather be low. I suspect that (too?) much moisture is produced here: laundry, plants, etc. Proper ventilation means, depending on the season, weather, and especially user behavior, sometimes airing out lightly 5 times a day instead of once.

Once you understand the connections and place a hygrometer, the issue will soon be resolved.

This morning I would have definitely had it too, but only after airing out. In autumn, the humidity outside is simply higher. You can't get rid of the moisture then because the humidity outside is higher than inside. If you also have cold windows because they are leaky or single-glazed, it's clear that the moisture primarily condenses on the windows.

Where are the wet towels dried afterwards and where is the rest of the laundry dried? If inside the apartment, can the laundry possibly be dried elsewhere? Alternatively, get a dryer.

Which is only partly true, warm air inside transports significantly more moist air outside than the much colder outside air can bring in. If the cold air then warms up, it can absorb more moisture.

I suspect that too much moisture is being produced here: laundry, plants, etc

- Warm bathroom air after showering gets into the other rooms? Keep the bathroom door closed at all times!

- the classic: room humidifier?

- The heat sources in the primary living rooms have to heat unheated hallways/toilets/guest rooms because the heating is turned off there?