You keep asserting that CRT displays were not and are not an issue, and they have flickering screens. Do a quick Google search for this and see if that stands up. Lots of people have issue with CRT displays......
Also, people used to talk about eye strain issues with watching too much TV or using computers in the 80's and 90's, but it just got dismissed with being either too tired or sitting too close to the screen. It may well have been the flickering.
And now we have a world filled with flickering lights with internal and external lighting, vehicle lights and instrument panels, TVs, smartphones, tablets and laptops. For sensitive folk, we are being bombarded with flashing light sources where ever we go which may not be seen but is most certainly felt.
And why is it I can spend 8hrs a day on an LCD iMac then follow up with 3-4hrs on my LCD iPhone and not have eye strain, but an hour on a OLED iPhone or device with known PWM and my eyes are strained and a headaches starts to form?
Sure, but is totally different issue, problems these days were "red eyes" so a lot of people needs to use drops in their eyes, the focus problems and eye problems has only appear in recent years with the use of LCD TV, computers and Phones that flick less.
If you want to know if flick is an issue for you, just buy an old CRT and put a movie o it. The problem is that current screens flick less, more hz, and this creates a constant light in front of your eyes and you start to develop focus problems. In a screen that flick a lot, your eye is constantly refocusing, so this problems never happened, but some people develop "red eyes" if you were a lot of time in front of the computer in that time.
As I said, if this problem is important for you, just buy a old TV and see if the flickering is causing the issue. I myself during a lot of years started to feel problems in my eyes due long hours in front of a LCD, this go worse with phones in recent years. One day my monitor get broken and in the meantime I would buy a new one I used my old CRT for some days, and my problems started to mitigate amazingly since day one. Since this experience I have not used anymore a LCD, OLED or any LED tech, I use a projector now and I get rid of all my eye problems and can be literally all the day in front of a screen, because with a projector, the light is more natural, it gets reflected, not go directly into your eyes. If I use my phone, any phone, during a lot of time the problems starts to appears slowly.
My take is that our eyes loose the capacity to focus without the abuse of the outside muscles due constant use of LCD, so every time you need to focus once you loose that hability it creates a lot of discomfort and problems. Once you return into a flickering screen, the capacity is restored due to constant "exercise", so the problem gets mitigated as the outside muscles gets relaxed.
So if this problem is important to you just give it a try, because as I have said in the 80 and 90 there were no this type of eye problems and screen flicks a lot then. These problems have increase dramatically since the use of LCD with more and more Hz and more and more nits.