You can archive a repository to make it read-only for all users and indicate that it's no longer actively maintained. You can also unarchive repositories that have been archived.
/articles/archiving-repositories
free-pro-team
enterprise-server
github-ae
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repositories
{% data reusables.repositories.archiving-repositories-recommendation %}
{% data reusables.repositories.navigate-to-repo %}
{% data reusables.repositories.sidebar-settings %}
3. Under "Danger Zone", click Archive this repository or Unarchive this repository.
4. Read the warnings.
5. Type the name of the repository you want to archive or unarchive.
6. Click I understand the consequences, archive this repository.