Back in April of 2020, we got a single message strongly complaining about our default dark theme; and we took a survey and only 1 of 6 responders thought it was "horrible" (see reference).
Over a year later, we are asking the same question again in a new survey, since everyone has been using the dark theme for over a year. Please click and contribute; and if you want, comment in reply.
Personally I use the "Light" theme, as I'm not a fan of dark mode-type stuff in general. But that's just personal preference: there's certainly nothing actually wrong with our default "Dark" theme, or at least not that I'm aware of.
It's good we offer the light themes as a user configurable option, for sure.
The vast majority "so far" (in this quick poll and the last one) are supporters of the "dark theme" as the default here on this site, as we can all see.
Personally, I use dark themes on my iPhone (most all the time, day and. night) and have github set to dark theme as well. Most of my apps are all set to dark themes as well; and of course, I only use the dark theme on this site.
Also, my development machine on my desktop (macOS) uses a dark theme and when I develop code in Visual Studio Code, the theme is also dark (which is where I tend to spend most of my time, as you can see from my github stats).
I find dark themes much easier on the eyes, for sure; and feel like I'm getting a headache when I use any light theme on my desktop; and on my main 34" curved monitor, I always have it set to the mode which filters out as much blue light as possible.
LOL, I am sure I would be less productive writing code if there were no dark themes (like in the old days)!