You're right, I have no idea how to check. All I do know like I said is it didn't make a difference to my eyestrain one way or another flipping it to off. I have no idea how to go about actually checking. Need like a high speed camera or something?
Well disabling it in the Nvidia X Server Settings didn't make any difference to my eyestrain. With it showing set as "Disabled" in both the GUI and command line, I was still getting eyestrain. However I can't confirm if it's actually off.
It's like everything in Linux is so intense on my eyes. Even though my i1 Display Pro says everything is nicely calibrated, and in fact both Windows and Linux DO look the same in their calibrations, it's just something weird going on that is causing eyestrain in Linux. I did read dithering is supposed to "fake" 10-bit on 8-bit displays, which might explain the weird "intensity" of color I'm seeing.
Using Redshift for the time being to drop the color temp to 4500K helped a HUGE amount.