Users might not have groups for themselves by they do login and have their own account to view the dashboards right. If that is the case then the User Filters should be the way to go.
To create views, you should filter the dashboard the Manager should see the data and then click on 'View:Original' button on the Tableau Toolbar. Type in the Manager Name or anything that is easily distinguishable > Check 'Make it public' and 'Save'. So you will have that option available for everyone and users can pick their respective views from the list.
*If this helps, then please mark it Helpful and Correct to close this thread
No, their name is not there in Tableau Server, Neither in any group nor Individually.