GitHub introduced dark mode: https://github.com/settings/appearance
From sites I use, dark mode is supported on Twitter, Slack, GitLab, https://startpage.com, Gmail, ProtonMail. Some others, like Jira, doesn’t have themes yet, so Dark Reader is a solution but it makes the page load is a bit slower.
Yeah, a few months ago I had a post how researchers say that light mode is better for eyes but I can’t get used to it, my eyes definitely get tired of a white screen. Bad background lighting? Glasses? I’m not sure what’s the reason, I need a bit more experiments.