I prefer light mode most of the time, but where I am sitting is dark enough, often enough - that I need to switch off to mostly-dark mode. I'll keep whatever I am reading in a lowered brightness.

DARK READER extension for Firefox (and other browser) have a mode for both. You can set light mode with lowered brightness - white stays white, but is much less glaring.

Another anecdata key factor here is - too many people have their fonts set too small, myself included. I find that when I turn up the font sizes, my eye strains far less irrespective of my dark/light mode settings.