The correct option is ghcr.io.

GitHub Container Registry uses the host named ghcr.io for pushing and pulling container images. When you tag an image with this domain and authenticate to that registry your workflow will push to GitHub Container Registry rather than another service.

github.com is the website and Git hosting service and it is not a container registry endpoint, so tagging an image with this domain will not push to GitHub Container Registry.

docker.pkg.github.com refers to the legacy Docker registry for GitHub Packages that has been replaced by ghcr.io. It is deprecated which makes it less likely to appear as the right choice on newer exams.

docker.io is the Docker Hub registry domain which belongs to a different service and will not push images to GitHub Container Registry.

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