I've been, like many of you, having a lot of trouble with eye strain (pain in the eyes, headaches, brain fog, etc). In. 2015, I bought a 2015 MacBook Pro with retina display that I returned for a 2015 Air without retina display because of eye strain. I was able to use that computer but in the last 5 years I've had severe eye strain if I tried retina display Mac's and also with all external monitors I tried.
I've gone to many ophthalmologist, gotten multiple prescriptions (I don't use any glasses otherwise), tried blue light glasses and tried many many external monitors.
Last year my 2015 Air was just getting too slow and I had to find a solution. Tried buying a ThinkPad but got eye strain and returned it. Earlier this year, desperate for a faster computer, I bought a new MacBook Pro M1. I got severe eye strain and headaches. Tried it with multiple external monitors that also resulted in severe eye strain.
Being desperate I decided to try to see if I could get used to it. I used it an hour a day at first (which lead to headaches that I managed with Tylenol if needed), then gradually increased it to 2 hours, then 3 hours per day. Over the course of 2 months I gradually got more used to it and now I can use it virtually without any problems for a full workday! I wouldn't have believed it going in but somehow my eyes or mind has adjusted.
Your milage may vary, of course, but it may be worth it to some of you to see if you can adjust to a new computer by sticking it out.