If your employee has access to create posts, they also have access to assigning roles. To remove access of visibility, please follow the steps below:
Click the Configuration tab or Admin Menu, depending on how your system is configured.
Click Roles & Permissions then click the relevant role.
Click Edit Permissions then search for the relevant role you do not wish them to have access to and ensure its disabled.
📌Note: This removes access to view the roles on the Roles and Permissions page, as well as removing access when adding roles on a post.