Orca detected that a Root profile was used to list S3 buckets. Listing S3 buckets is a common enumeration action attackers conduct in the reconnaissance phase. The root account should not be used in day to day administrative tasks because it can't be deleted and its permissions can't be revoked. If its credentials will be stolen the entire account is at risk.
It is recommended to review the root account activity and eliminate the use of the root account by creating individual users with set permissions.