I saw @TThaCMaster mention in another topic it has to do with the gut. I agree with this. I've had chronic fatigue and autoimmune disease my whole life. Now I'm sensitive to modern screens and have a lot of food and gut issues.
I'm in the heal your gut guy Facebook group, I could ask there if anyone gets eye strain from newer phones/ computers.
The Heal your gut guy has completely changed his tune and is promoting German New Medicine (GNM) - https://learninggnm.com/home.html
Most of us are probably living in chronic stress so it would help to track conflicts and use GNM to help resolve these things.
Also I have a feeling our condition relates a little to epilepsy and brain conditions (Likely caused by malnutrition due to gut issues). The keto diet was created back in the 70's and it helped children with epilepsy.