I wanted to follow up on my initial post, in case it is of help to others.
PWM and/or OLED brightness was not the underlying cause of the issue I was having, and rather the tendency of OLEDs to cause eye strain seems to have made existing eye conditions I have/had more problematic.
I went to a REALLY good eye doctor. I was diagnosed with two things that no eye doctor to date had ever diagnosed. The first is MGD, or Meibomian Gland Dysfunction, which is a cause of tear film instability and hence dry eyes. It is closely linked with frequent computer use, eye strain, and contacts, which I wore. The second is a very mild case of amblyopia, which is linked with headaches. I also had astigmatism, which is linked with eye strain and headaches. The combination of these factors were what was causing me a lot of issues. OLEDs seem to have further inflamed things.
I was able to get the MGD under control by doing about 8 different things. Then I underwent a permanent vision correction procedure called ReLEX SMILE, which is effectively a less invasive alternative to LASIK that has some pretty significant benefits for those with dry eye issues. This procedure permanently removed my astigmatism.
This seems to have fixed things for me.
FWIW and IMHO, if PWM seems to be causing an issue, if you haven't already, it's definitely good to be sure there isn't something else at play (and something that might be very fixable, for that matter), whether it be eye issues or something else.