In all versions of GitLab CE/EE since version 13.6, it is possible to see pending invitations of any public group or public project by visiting an API endpoint.
{
"cpes": [
"cpe:2.3:a:gitlab:gitlab:*:*:*:*:community:*:*:*",
"cpe:2.3:a:gitlab:gitlab:*:*:*:*:enterprise:*:*:*",
"cpe:2.3:a:gitlab:gitlab:4.3.0:*:*:*:community:*:*:*",
"cpe:2.3:a:gitlab:gitlab:4.3.0:*:*:*:enterprise:*:*:*",
"cpe:2.3:a:gitlab:gitlab:*:*:*:*:*:*:*:*"
],
"severity": "Medium"
}