Before I spin up an environment to investigate this, can you confirm what you mean by "not available for the agent to select"?
Are you referring to the Status property of "User Selectable" or Access Control settings that allow you to limit which users get to use which statuses?
I need to check, but from memory, a Status needs to be "User Selectable" for any user (including Supervisors) to select it, but if it isn't on the list for the Agent, they won't be able to select it (and, I hope obviously, the Supervisor would need to have it on their list!)
HTH