Hi @vladob,
GitLab is added this feature in v13.x, where GitLab notify users by mail if a sign-in occurs from an unknown IP address. By this way GitLab alerts the users of potentially malicious or unauthorized sign-ins.
As of now there isn’t any option given to disable the above feature. Similar open issue also has been reported by Jasper honig- https://gitlab.com/gitlab-org/gitlab/-/issues/218457
Regards,
Kaushal