I’ve found an issue where it said that the rake task for the root account might not work, and should use Reset a user's password | GitLab instead.
It could also be the case that the root user is disabled. This is common security practice to avoid exploits,. I have shared an alternative approach with 2FA in Block built-in Administrator user - #3 by dnsmichi
Maybe the root login is also tied to LDAP/AD/SSO (through email or other fields) and does not allow resetting the password.