Recent research is finding out that dark mode, or at least a number of variations of it, are worse for your eyes than simple fully lit. It has to do with some of the options to dim the screen, which then create a flicker that may give you headaches or other ill effects. This has been an area that has come under scrutiny for a while, as people report some better battery life, but others notice no difference. Personally, I prefer the fully lit mode, as I escaped the old amber and green screens of the late 80’s and have no desire to return. I do throttle my brightness back to about 50% or lower as I don’t feel the need to wander around with a big flashlight all the time.
Dark mode is supposed to be easier on the eyes, especially at night, but modern smartphone displays and dark modes don’t mix as well as you think.