My OnePlus phone in direct sunlight not only pushes the physical OLED brightness to the max, but seems to also apply some filter to the image that makes dark colors brighter, e.g. a dark gray keyboard almost turns into lighter gray. Does help with visibility.

I agree, I'd rather not have to turn the brightness up to 100% so that my battery life drains faster to be able to view my phone in direct sunlight.

Turn 180° and the problem is solved.