If you see the floaters then your screen is way to bright. I see my floaters only when looking at the sky during the day and I have lots of them. I think this is because the pupil contracts and the depth of field grows and the floaters project onto the retina
I think the popularity of dark mode is at least partially because people's monitors set way too bright.
It is possible, but it is also about preference and the need to occasionally make change. Sometimes it feels cool to have a different environment. I used to enjoy tinkering with this kind of stuff a while ago. Now not so much, I try to go with defaults or minimum changes.
I can see mine even on minimum brightness... I just happen to have a couple of pretty dense, yet small, ones.
It's hard to compare the floaters, I think I have many when I look at a bright lit sky but you may as well have/see/perceive way more. Gotta add that I am not wearing any glasses but my eyes (blue) have always been super sensitive to light, I'm one of those squinter when I forget my sunglasses. I find that cloudy days affect me as much as sunny days if not even more since the light is not coming from one direction I could avoid, it seems like it's coming from everywhere.