uchar I've changed my hypothesis a number for times, but at this point I would say Nvidia and laptop displays don't communicate well recently (external displays are fine, until a Linux kernel update messes things up). Upgrade to Ubuntu 22.04 tells me the situation can be regulated (although not definitely solved at this moment) on the software side, but it seems to be OS- rather than driver-dependent (the same driver versions give me eyestrain in 20.04, but not in 22.04). At the same time, I also get eyestrain in bios, so it's either Nvidia firmware, or some other firmwares, or a hardware problem (I'm still reluctant to admit it's the problem of eyes). Still - the timespan and commonness of the issue among various laptops is incredible…
EDIT: Do you have anything like "GPU performance scaling" in your bios? I turned it off in Clevo (in my Legion there is no such option), and it seems the display is even more bearable. Again, it seems less Nvidia -> less eyestrain.