Answer

When the Laptop with an OLED panel is turned off, the screen may not look completely flat, especially when viewed in reflections.

This is the inherent characteristic of OLED technology. The OLED panel can be very thin since it doesn't need a backlight module like traditional LCD, and the organic light-emitting layer is very slim and flexible, so the surface of the screen may look uneven and appear distorted or wavy in reflections. It's not a defect and won't affect the functionality or image quality.