I have been using the iPhone 12 since it was released. Every year, I try to switch from it, but it remains the best for my eyes. I use the regular version of the iPhone 12, as others are not suitable for my eyes. I always keep the brightness at 100% and have the power-saving mode on (it makes reading easier for me as the screen becomes slightly less bright). In this mode, I can use it indoors for up to 30 minutes at a time, and outdoors in daylight without any time restrictions. Unfortunately, reducing the brightness from 100% or lowering the white point makes it less usable for me.
The last iPhone I tried was the 15 Pro, and I couldn't use it even outdoors in daylight; by evening, my eyes hurt a lot.