Gitlab – Project cannot be transferred, because tags are present in its container registry

Issue 33301 mentions:

the only way to move a project with containers in the registry is to first delete them all.

Meaning delete the container tags in the registry (not the repository or CI/CD)

• Navigate to sidebar menu Package->Container Registry on a project where Container registry is enabled
• Click on the button “Remove Tag”

(since GitLab 12.3, Sept. 2019, you can delete the tags you want)