My eyes don't get tired even after many hours of coding with dark background unlike with white. I actually use complete black wherever I can. It surely has to do with the amount of light emitted. Even on my phone I keep the brightness to less than half.
Anyone with an iPhone and likes dark mode should go to settings and enable smart invert (general > accessibility > display accommodations). Then go to general > accessibility > accessibility shortcut (scroll all the way down) and choose smart invert.