To provide information regarding adding local users in VMware Cloud on AWS vSphere environments.

VMware Cloud on AWS

The "cloudadmin@vmc.local" user account is a local user account with administrative privileges. 
This account has the privileges needed to create and manage the SDDC workloads and cannot be modified.
Additional users with more restrictive privileges are needed. 
The "Add" button in the Single Sign On > Users and Groups section is grayed out. 

In VMware Cloud on AWS environments, the "cloudadmin@vmc.local" account is the only local user account available. 
Additional local users cannot be added. 
If additional users are needed, please follow the process to create an Identity Source and add permissions for Active Directory users and groups: Add an Identity Source to the SDDC LDAP Domain

vSphere Permissions and Privileges in VMware Cloud on AWS