Dark but I change to light when I have to have a zoom meeting where the dark background darkens my screen and camera picks up that I’m doing something else
Dark themes are just inherently less harsh on eyes that are fixated on them for hours and hours every day, regardless of ambient light situations. That might help a bit if you're used to looking at things in a darkened room, but I sit at a computer all day in a brightly lit environment and have no issues with my eyes, but I feel like I get screen burn on my retinas looking at stark white windows all day, it's just too much.
Its an extension of the analog world using white paper with black ink, but translated to luminescent mediums, this becomes uncomfortable over long periods, we don't need to do this anymore. Dark mode is the future.
Thats why avatars are important. Without that you don't even know who are you talking to on whatever subject do you think they're talking about because you can't see any text at all.