For global policies defined at the root organization level, you'll find that you cannot add notifications, to it, at the organization or application levels, the UI will be greyed out.
To work around this, we can use the Role Recipient Type, for sending application level notification.
We can use the inbuilt Roles (Owner, Application Evaluator or Developer) and add users accordingly.
If you need to send notification to users without any access, define a new role in Nexus IQ Server that will be used for the notification. Edit the policy in the root organization, and assign notifications to the new role.
Then in the corresponding application, select "access" settings and then "add a role". Choose the role you just created, and assign uses to this empty role.