Window leaking and mold - window sill is cracking

Hello everyone,
since the completion of our house (built by a developer) 4 years ago, we have had problems with the windows on the east side.
Water runs inside onto the windowsill and it is being damaged. The inside surfaces of the windows are molding.
We have already pointed this out to the developer several times, who believes it is our responsibility to ventilate twice a day to prevent these problems. Our warranty expires next year, and we want this issue to be finally resolved.
Is it worth having an expert come by and insist on replacing or readjusting the windows, or is nothing to be done here and we have to accept the ventilation situation as it is?

I would be very grateful for your opinion.

Hello,

I would suspect both condensation and water from the outside.

There is a drip edge at the bottom of the window (last picture), where water entering from outside can drip off and drain outward through the intended openings (6th and 7th picture). No fault at this point.

However, the gap in the outer seal, especially on the underside, is problematic. There, the drip water can penetrate into the interior of the window. In addition, cold air enters and condenses.

Equally problematic is the bracket of the interior roller blind or pleated blind. Due to this bracket, the sealing rubber obviously no longer fits tightly against the window frame. The moist, warm air presses from the bathroom outward (overpressure), condenses, and causes stagnant water.

Honestly, the windows don't look particularly well maintained, so my assessment is that you also bear some partial responsibility for the condition. In the fourth picture, the window is heavily fogged up, something that must be aired out. You can try to focus on this gap in the outer rubber and argue accordingly.

Best regards