You can force light themes instead and flip the colors in KWin. This will make t...

You can force light themes instead and flip the colors in KWin. This will make text look worse than doing it in CSS, but it's basically free performance-wise.

https://github.com/natask/kwin-effect-smart-invert

Aside from that, I found that using blue light safety glasses (e.g. Uvex) reduces the pain I get from white flashes significantly.