My device is already in dark mode but I will see what happens when I use that chrome flag.
So now reduce the brightness.
Modern smartphones, as is the idea that everyone will watch 4K videos all the time, always set the colors and light to maximum, so that the person can have a "fantastic experience"... But, I don't watch 4K videos on my smartphone. So reduce all the extras, besides saving battery, save the most important thing - my eyes!