@astfarazt The access to the case object is controlled by both settings, Restrictions connected to the Case Type and the Access Restrictions per user or user group in Case Access Group.

In your case if the Case Type is Global that means probably the Restrictions set to None.

In that case, if a user wants to see a case, the user should be the creator of the case or else should be added to the Case Access Group as a user or a group where the Access Restriction is None. This is the normal setup for call center connected employees where we need less restrictions.

Hope this helps !

Thanks @Buddhika Kurera .  Seems I misunderstood that both settings apply.  

One other related question, if a Restriction of Customer is defined, where do you connect the Assignee to one or more specific customers?  

@astfarazt In the Customer setup, the users connected to the customer can see the cases. Therefore try adding the users to the customer as a B2B users then such user should see the cases connected to the specific customer.

Thanks for the response, much appreciated!