Can the Settings system app be blocked or hidden?
Apple does not currently allow the Settings app to be blocked or hidden from the user, under any condition.
Despite this, it is possible to create a home screen layout and place the Settings app on a separate screen or in a folder, making it less visible. Home screen layouts are available for supervised devices only. This page provides more information about home screen layouts.
If your desire is to prevent a user from modifying Apple ID or other account settings, it's possible to restrict the user from changing these. Simply uncheck "Allow account modifications" from the restrictions tab in the Group details screen. This feature is also only available for supervised devices.