I will be using Lagom monitor test to test dithering. Especially the page on Contrast to see if banding can be observed. If banding can't be observed, then dithering is likely in effect.
http://www.lagom.nl/lcd-test/
My iphone 8 is on iOS 14.5.1. Banding can be clearly seen on the Contrast page.
My iPhone XR is on iOS 16.2. Banding can be clearly seen on the Contrast page as well.
I think these results indicate that dithering is not used in iOS 14.5.1 or iOS 16.2, at least not for iPhone 8 or iPhone XR, making these phones safe for my eyes, in combination with the use of LCD IPS screens.