Meltwater in the window frame of new wooden windows

Dear forum,

I hope you can give me advice on the following concerns:
Last year, new wooden windows were installed in my 1950s old building. The entire building was completely refurbished. The upper floor was fully insulated to KFW standard, the basement has no insulation under the supervision of a thermal protection expert/structural engineer, but somewhat more "permeable" windows.

Now that the frost is here and also last year, there have repeatedly been "problems" with water standing in the frame. According to the window installer/joiner, this is not a problem. However, it worries me quite a bit.

The windows are adjusted and sealed. I have already tried to add a seal on the inside as well. However, then I cannot close the windows at all.

Does anyone have advice – I would be very grateful, as I am completely clueless...

Additionally, on the seals of the casement doors there are small white plastic plates. Are these necessary? Most windows are missing them.

Do you get a sheet of paper passed through when it is closed? Yes, adjust it regardless of what the window fitter says.

Yes, I had thought about that too. But I have to press the windows shut really firmly to close them. The sheets of paper hold tight as a drum…

Condensation from showering and cooking? What does the hygrometer say?

Presumably kitchen and bathroom? How high is the room temperature?

That is actually in all rooms on the [OG]. I have set the room temperature to 17-18 degrees. Some of the rooms are simply not yet occupied.