That’s fair, i’ve had used a few apps for long periods of time with light mode and it is pretty nice, although i’m biased towards dark mode. Maybe it also has to do with the enviroment around you? Since a dark theme while outside in a sunny day would surely put some strain in your eyes?
That does work to lower the strain in your eyes (coming a person that has had one in their phone for years now) but as far as i know, that is mostly meant to lower the amount of blue light coming from your display, as to not affect your sleep cycle
edit: typo