machala Dont feel bad about your setup, because there is no way of knowing what you can get used to and what not. Dont feel bad about money being wasted, some people will buy cigarettes for more than 1000€ a year but we are trying to do sth beneficial to our health. 
Well it is more than one thing that strains my eye, but a bad device stays a bad device. I think my two Eizo monitors are a weapon. They are meant to be flickerfree, but they do some very fast flickering(up to 50.000 hz and more) on the background lighting settings i use(someone measured it on a recent device). Going to 100/100 brightness doesnt make it better, i tried it and always get immense back pain in the back of my eye using them(harder than any other device i ever used or tested). I also have a BenQ 32 inch that causes only mild eyestrain because no PWM at all, but causes me naseau, but it is better when i use it on a lower resolution centered in the screen(making it more or less a 24 inch screen that way).
My first problem is PWM. For example i am symptomfree with my 5 year old HUAWEI phone, i use it a lot. I can use it in total darkness without eye strain. I have to do this because i have to wait 10-30 Minutes until my son falls asleep. But there is a brightness setting, that the phone wont toggle down to on its own, you have to force the phone. As soon as i do this by force(put the slider all the way to the left) it is becoming straining. I am sure my eye is not liking it, because it is more flickery that way. I also have a LG TV and i can see the 120hz flicker with my bare eyes when going lower than 50/100 on SDR content. But this can all be solved, there are a lot of flickerfree DC-current monitors out there.
My second problem could be GPU/Mainboard/softwarerelated. I just looked at my step mums Iphone 13 and it crashes my eyes. My workphone is an Iphone X and it is not causing me symptoms. I think both are using White OLED, so this shouldnt be screen related. They Sony OLED i tested gave me super weird nausea, it is the same screen size as my old one. All picture optimizing was off, it was totally ok in the store. I still think OLED is the way to go, but perhaps i will try a LG 55B2 next, but only after i found a suitable monitor. It is impossible to test anything with a suboptimal monitor.
I also use up to three devices(PC, worklaptop, steam deck) with the same monitor(i now never use more than one monitor at a time, because it is too many variables). Symptoms are slighty better with the Intel, but until i have an optimal monitor i think i cannot pinpoint(flickerfree, responsive, 24 inch max, TN-Panel colors, sharpness setting to play with). I think it is about font rendering, but i am not sure.
My next test is the LG 24 GL600F. One of the users in the forum tried it and he never said a bad word about it again(he was active months after getting it). I also searched for people complaing about "eye strain", "strong reds", "flicker" with this monitor, but only complain seems to be with freesync, which you can turn off. It is worth a shot, it is 174€, which is like going to the restaurant 3-4 times in my country. Rtings review below.
https://www.rtings.com/monitor/reviews/lg/24gl600f
My last problem is lighting, but i use a lot of daylight and it is near impossible to find out which lighting i prefer, when i dont have a working monitor. I know that some HUE lamps seem to be bearable(hue white and color) and other HUE lamps i own are sh*tty garbage(hue white).
I am also thinking about getting an old monitor without LEDs inside but with an HDMI port. But my wife is killing me with her nagging about all the stuff i already bought, so will try the LG 24GL600f first.
If the monitor is better i will try to get a cheap used laptop with a safe GPU and a working docking station(i have one, but not sure it will fit a used laptop). Used laptops can be super cheap and i am totally fine to use PC only for gaming and a safe laptop i can do all my work stuff on.
You seem to not have problems with your monitor? What are you using right now?
