I suspect the temporal dithering technology was introduced since ios 15 and was much worse since ios 16.
My ipad air 2 was made useless since the upgrade to ios 15, while my iphone se 2020 got a little more uncomfortable to look at on ios 15. And ios 16 was the final nail to the coffin that made my iphone become useless (my ipad air 2 does not get to have ios 16 update, but it is already useless anyway). My devices are all LCD display ones so PWM will not be the reason of eye strain here, and I could use them comfortably before ios 15-16.
This is not the first time I’ve seen people talking about the same idea. Many devices suddenly became useless after ios 16 upgrade, according to multiple posts online.
My iphone right now is on an ios 17 beta version and I can confirm that the eye strain still persists, so anyone on any ios version of 14 or earlier should NOT try to take the risk of upgrading your ios to any newer version. Stay on ios 14 or earlier versions to be safe. Also if you want to purchase a legacy iphone or ipad, you should check which ios version it will run on. If you buy a device which has ios 16 out of the box, it is very likely to be a wrong purchase.
I can’t believe why Apple is allowed to make such a radical change to the display rendering and not make any statement about it anywhere.