One of the most urgently asked for feature in TrueNAS is the addition of rootless login to the TrueNAS GUI and the provision of a “non root” administrator account for more security. This seems to have finally arrived. As you can read in the latest version of the TrueNAS Scale documentation:

Only the root user account can log in to the TrueNAS web interface until the root user creates an admin user with the same permissions. After logging in as root, TrueNAS alerts you to create the local administrator account.

As part of security hardening and to comply with Federal Information Processing standards (FIPS), iXsystems plans to completely disable root login in a future release.

System administrators should create and begin using a new root-level user before this function goes away.

Found at: https://www.truenas.com/docs/scale/scaletutorials/credentials/managelocalusersscale/