Long shot, but isn't A-FRC a type of software dithering occurring at the monitor (vs. OS/GPU)?
Only reason I bring this up: I had used two external monitors on my zbook forever. The laptop had 6bpc depth by default on its native screen, and that carried over to the external monitors. One day, I made the mistake of setting them to 8bpc, and the nVidia control panel wouldn't let me revert! Swore I had eye strain issues thereafter.
I swear a lot of these issues coincide with the move to 8bpc+, and a lot of monitors are not yet 8bpc native (it's 6+aFRC). I wonder if something similar happened here - defaulting to a higher color depth that forced flickering.
I have no idea if something native to the 8 bit color "palette" is what bothers my eyes or just the flickering that gets us there, but I suspect it has something to do with that on modern software & hardware. In any case, good luck :/