Currently, when a Manager role is turned on in the user profile, they will not see any of their direct reports in the Manager Experience unless they are manually added in the User field. If the Manager role is turned on and assigned then they should automatically see their direct reports without having to add them manually.
If this is not how it works, please update the documentation to provide more clarity on how to use this functionality.
Be great to have the option to simply select "Managed Department" as opposed to manually entering every direct report. Some managers have in-excess of a 100+ staff. Often multiple managers need to see the same staff.