You are comparing GitLab (the application) with codeberg.org (the website operated by the codeberg e.V. non-profit). A fair comparison would be gitlab.com (the website operated by GitLab Inc.) with codeberg.org or GitLab (Community Edition or Enterprise Edition) with Forgejo (the application powering codeberg.org). They can be fully self-hosted and are both planning to implement AcivityPub-based federation.