So, I ran around with a circular polarizer filter and examined a bunch of screens from both categories (both those that I can use for hours a day without a problem, and those that cause me painful eye strain and other symptoms with minimal use). Unfortunately, I found examples of each in all three categories, so I do NOT think polarization is my issue. Below are some examples. The items I list as "GOOD" below are screens I can use all day without an issue, the items I list as "BAD" cause my terrible eye strain with minimal use:
Horizontal polarization: Dell P2014HT 19.5" monitor (GOOD); Motorola One 5G Ace cell phone (GOOD); Samsung LED backlit TV Model UN55TU8000FXZA (GOOD); Sony X85K 43" TV (BAD)
45° polarization: Asus VS247H-P 24" monitor (GOOD); Asus VG248QG 24" gaming monitor (BAD)
Vertical polarization: 2022 Chromebook (GOOD); MSi Optix G273QPF 2022 27" gaming monitor (BAD); a couple other modern gaming monitors I tested (BAD)