We use them in our shop. It's quite straightforward if you're already familiar with Github Actions. The Forgejo runner is tiny and you can build it even on unsupported platforms (https://code.forgejo.org/forgejo/runner) e.g. we've setup our CI to also run on Macs (by https://www.oakhost.net) for App Store related builds. It's really quite a joy :)

Are you building MacOS apps? More specifically, are you doing code signing and notarization and stamping within CI? If so, is this written up somewhere? I really struggled with getting that working on GitLab. I did have it working, but was always searching for alternatives.