Screen backlight dims in sunlight

I’ve seen this issue across both mine and my friends’ iPhones, I’m an engineer at Google and have checked the obvious: ie. auto brightness settings and True Tone settings which aren’t the cause here.

Whenever an iPhone is in direct sunlight (and heat?) the backlight dims fully and makes the screen unreadable. This is particularly frustrating when flying drones etc when you need the screen the most. Definitely a bug in the OS as I’ve checked all settings.