Gen X woman here, I started using dark mode a couple of years ago when I was really suffering from Long Covid, and using any kind of screen was a trigger for fatigue so bad I'd need to go lie down and sleep before I collapsed. I read up on managing screen work with fatigue conditions, and dark mode was suggested. As soon as I tried it it was like loads of noise went quiet in my brain, and it just felt calmer. I also suspect I may be autistic and / or ADHD and this may also be a factor. I have to have everything on dark mode now, light mode just feels so shouty and loud.