Seat Ateca Rain Light Sensor Issue

That does sound like the rain-light sensor. The speedometer dimming issue also points to a central electrical fault related to that auto sensor. Have you checked for any damage to the windshield around the sensor area? Any recent windshield replacements?

No visible damage to the windshield and it hasn't been replaced. But, you mentioned a 'central electrical fault'. Could you elaborate a bit on that? I'm curious if there are other car components tied to the sensor that could be affected or if it's purely localized to the sensor itself.

Since there's no visible windshield damage, it strengthens the gel pad theory. By "central electrical fault", I mean that the rain-light sensor is tied into the car's central control unit. The sensor provides data that influences several other systems. It's possible that a faulty sensor is sending incorrect signals, leading to these issues. You should definitely take it to a workshop to get the sensor checked and potentially recalibrated. They can confirm the gel pad issue too.

Took the Ateca to the workshop. The gel pad had bubbles, causing the light sensor fault. A new gel pad and sensor calibration fixed everything. Total cost was 62€, a relief. Thanks for your help!