What action must an administrator perform in the vSphere Client to create a VM template usable by multiple vCenter Server instances?

To create a VM template that is usable by multiple vCenter Server instances, the administrator must clone the virtual machine into a template and store it in a content library. By selecting the option to "Clone as Template to Library," the template is created in a shared content library that can be accessed by different vCenter Server instances.

Content libraries play a crucial role in vSphere environments by enabling the efficient sharing of templates, ISO images, and other files across vCenter Servers, enhancing management and deployment efficiency. This method eliminates the limitation of templates being restricted to a single vCenter, allowing for greater flexibility in managing resources across multiple sites.

Other options do not achieve the same result, either by targeting a local storage scenario or converting an existing template back to a functioning virtual machine, thus not serving the purpose of creating a template meant for multi-instance use.