Mobile users say that they can no longer activate Dark Mode on Facebook, and there's no explanation why.
Facebook Dark Mode just vanished — what we know : Read more
Facebook Dark Mode just vanished — what we know : Read more
The same thing happened to me. But I fixed it by logging out and then back in. My dark theme came right back after I logged back in.I am an Android user and I lost it suddenly around that time too. Had an update, tried that, still gone. My groups and videos buttons are gone too.