One possible explanation might be the use of display panels from different vendors. I first noticed eye strain /pain from a Macbook Air in 2012. It had an LG display. I ordered another and got one with a display made by Samsung. That one was okay. No eye strain or pain. At one point I remember getting one with a display made by AUOptronics, which also gave me eye strain / pain.
There used to be a command that would show which display panel a macbook had. It seems apple has disabled command that in Monterey.