Hi! In general, we recommend (and support) running the github-pages gem with the Ruby version we're running in production (2.7.x). We don't yet support Ruby 3.0.0. Ruby 2.7.x still has webrick so I'd recommend using that until we've upgraded for your GitHub Pages needs!
per https://github.com/github/pages-gem/issues/752#issuecomment-764758292: