The primary monitor I am able to use successfully is an Asus VS247H-P (23.8" 1080p TN panel) monitor manufactured in July 2012 (the manufacture date is marked on the back). Since I've had such a problem finding monitors that don't trigger my eye strain symptoms over the past ~8 years, I had purchased two backup copies of this same Asus VS247H-P model: one copy manufactured in January 2015, and one copy manufactured in August 2018.
The Asus VS247H-P copies built in 2012 and 2015 cause me no symptoms, I can use them for 8 hours a day no problem. But I discovered that within 10 minutes the Asus VS247H-P built in 2018 causes the serious eye strain symptoms that I experience with all modern monitors! What's more, the colors of the 2018 Asus VS247H-P are noticeably more vibrant than the other two, even though the monitor is the same exact model and specs on paper.
I intend to keep digging to see if I can determine what changed- because whatever they changed causes my eye strain symptoms! I currently suspect the broader color profile somehow enabled in the newer copies is achieved by dithering (as I have also experienced my symptoms with non-LED flickering projectors). But meanwhile just felt it was worth mentioning in case it helps anyone that even within the same model# the technology has changed.