I am looking for a way to create new user Display.
When I go to Admin > Configuration > People > Acount Setting > Manage Dispaly
there are only three display modes: Default / Compact / User Account
How do I create a custom display mode?
See attached picture. 
On the page shown in the screenshot (Administration > Configuration > People > Account settings > Manage display or /admin/config/people/accounts/display) click on Custom display settings. It will show further settings, including the Manage view modes link.
Click on the Add new mode button.
Click on User
Enter the name for the new display mode, and click on Save.
When you go back to /admin/config/people/accounts/display, you will find the new display mode listed together the other ones.
In drupal 8 you can easily create a new view mode via backoffice : Administration > Structure > Display modes > View > User
and click Add new User view mode.
To go further see documentation : https://www.drupal.org/docs/8/api/entity-api/display-modes-view-modes-and-form-modes
