User with Administrator role is added in Subscriptions > example.com > Users. However when logged into Plesk Tools & Settings menu is absent, UI is locked in Power User view and cannot be changed, and particular website settings, such as Additional Apache directives and Additional nginx directives) are missing in Plesk interface.
By design, user added via Subscriptions > example.com > User has limited set of permissions. These users are not considered to perform the same actions that Plesk administrator is able to.
If it is required to create user with Plesk administrator privileges, create Additional Administrator Account as described here.