The most optimal operating system for use by a team of remote workers that need to access classified secured files and documents would be a network operating system.
Network operating systems are designed to manage network resources and enable multiple users to share files and communicate over a network securely. They offer features such as user authentication, access controls, and secure file sharing, which are crucial for handling classified information.
Distributed operating systems can also be suitable, as they manage a group of independent computers and make them appear as a single coherent system to the users, but in the context of remote workers accessing shared documents and files, a network operating system is more directly aligned with the needs described.
So the best choice here is network operating system.