An issue has been discovered in GitLab affecting all versions starting with 7.1. A member of a private group was able to validate the use of a specific name for private project.
https://hackerone.com/reports/605608
https://gitlab.com/gitlab-org/gitlab/-/issues/12560
https://gitlab.com/gitlab-org/cves/-/blob/master/2021/CVE-2021-22193.json