For a few years I used dark mode because i thought it was better for your eyes; it isn’t.
When in dark mode, you’re looking at an overall darker screen, your pupils will dilate to let in more light, which makes everything just outside of focus very blurry, and gives the text a halo effect. A few minutes will be fine, but anything longer is going to make your eyes begin to strain.
When in light mode, your pupils contract to accommodate for the light, this is how our eyes are supposed to work, this is going to be less straining on your eyes. In low light environments, simply turn down the brightness and apply a night light filter.
If you’re going to use dark mode regardless, don’t use AMOLED unless it’s for saving battery. The contrast between bright white and pitch black is the worst combination. Consider using a soft grey, your eyes will thank you.
Depends what you’re doing. If you’re not doing intensive reading it’s okay. If your eyes are more tired with light mode, it just means the night light filter, or the brightness isn’t adjusted right.