I've been reading the ledstrain.org threads over the past several months and the consensus seemed to be that only the earlier W10 versions like 1511 would be comfortable for visually-sensitive individuals but I was never able to get a copy of this. I had significant eyestrain/mental fatigue issues since "upgrading" to an i5-6500 based desktop a couple of months ago. But I think I found a solution that can hopefully help others and that is using Win10 Audit mode.
The solution for me was rebooting in "Windows 10 Audit Mode" ; typing : "%windir%\system32\sysprep\sysprep.exe /audit /reboot" after running CMD (command prompt) reboots the computer to Audit mode and it changes (on my PC) the rendering (or how Windows functions with the display driver) and it substantially reduces (or nearly eliminates) the eyestrain/headache/mental fog symptoms I've been experiencing with my i5-6500 PC since late summer.
I'd previously been using Windows 7 in VGA Basic adapter mode (Intel HD4000 disabled, as enabling the driver would always cause headaches) at native resolution on an older Haswell based laptop. I also was using a separate pre-Haswell (2012-13) desktop running Intel graphics (driver enabled) through the VGA output (not DVI or Displayport) and it was also good with Win7. Both configurations were very comfortable at 100% hardware brightness to suppress PWM, but I needed a higher-performance computer running a more current version of Windows.
I had purchased an i5-6500 based desktop running Windows 10 in late summer (preinstalled with version 1811 I believe, but later upgraded to 2004, 20H2 and then 21H1) but I had been grappling with eyestrain, reduced mental focus and ringing in the ears whenever I used this "newer" PC with all of these Win10 configurations, since the first time I tried using it. I've tried three different 4K monitors (LG 27UK500, Benq EW3270U, Lenovo L28U-30) along with my 10+year old TN FHD monitor (which was fine with the older PC running through VGA/analog output) with this i5-6500 PC (running Displayport via the integrated 530 graphics, or HDMI through a separate Nvidia 710 graphics card I purchased to see if it would help) and I would still get the same symptoms. Some days were better than others but it was never nearly as comfortable to look at and use as my 2013-2014 PC and laptop. The symptoms were slightly worse when I was running through Integrated Intel 530 graphics enabled, but they were still noticeable with the Intel driver disabled (ie running through Microsoft Basic Display adapter or VGA mode at native resolution). The Nvidia graphics card didn't make any real difference, either.
I even tried installing Windows 8.1 and Windows 7 on this i5-6500 PC and I used it with Intel 530 drivers enabled or also with the Intel530 disabled (ie Basic Display adapter mode), and it was never fully comfortable either way; it was perhaps marginally more comfortable than Win10 but no where near as comfortable as my older 2012-14 Win7 desktop and laptop. I was disappointed that even "trusty" old Win7, which had been very comfortable on my older 2012-14 laptop and desktop, was still providing symptoms with this i5-6500 PC, regardless of which monitor I connected it to. I also ran the monitors at 100% brightness to eliminate PWM. On the side, I don't believe most of the newer monitors advertised as "Flicker-free" have true unchanging illumination intensity at sub-100% brightness; from my own experience, I would always experience additional eyestrain or headaches at brightness levels under 90-100% settings, even on monitors advertised as Flicker-free or as using DC modulation to control the backlight. And I'm certain it's not placebo.
Somehow I read about rebooting Windows 10 in Audit mode and I tried it and to my great surprise and relief, it felt immediately more comfortable....and this is with the Intel HD 530 graphics driver ENABLED. To my great surprise, running this system on Windows 10 21H1 in Audit mode with the Intel 530 Graphics enabled is much more visually comfortable (and provides better mental endurance and clarity) than running the exact same hardware (4K monitor Displayport native resolution) with either Intel 530 graphics driver enabled or disabled (Basic Video Adapter/VGAadapter mode) on Windows 10, 8.1, or Windows 7 at the same 2160p resolution. I can't explain logically why this works since I'd assumed that Windows 7 or 8.1 running through the Basic/VGA adapter would cause the least additional image processing, but apparently not. Apparently the Win10 Audit mode, at least on this i5-6500 setup, gives the cleanest most comfortable image.
Anyway I just wanted to share this with the group and perhaps running in Win10 Audit mode will provide much needed relief to some other people as well.