Mlem has dark mode. It follows your system settings

Hi! So glad you’re using the app. Feature requests and bug reports should either go to the GitHub issues or to the release post.

I use Firefox and I have Dark mode. I think it is a setting in the browser, but I cannot remember what I did as I did it years ago. Edit: and I deleted my comment instead of editing it. I do not use any apps as I only use my PC for any social media.