A domain user is able to successfully log into the vSphere Web Client, but notices that the vCenter Server system does not appear in the inventory. Which is the cause of this situation?

The Service Control Agent manages vSphere services at a platform level, and if it were not running, all users would experience service failures rather than one user seeing an empty inventory.

Having no hosts added would result in an empty Hosts and Clusters view, but the vCenter Server object itself would still appear in the inventory for any user who has permissions on it.

Read-only permissions still grant visibility into the inventory; the user would see vCenter Server but be unable to perform write operations on it.

In vSphere, authentication and authorization are separate concerns. A domain user can be authenticated via SSO and reach the Web Client, but if no permissions have been assigned to that user on the vCenter Server object or its children, the inventory remains invisible. Permission assignments must be explicitly made on vCenter Server inventory objects to grant visibility and access.