Hi,
Global Admins is not Azure RBAC role. Global Admins is Microsoft Entra role. By Default Global Admins do not have access to Azure subscriptions but they can elevate themselves and gain access to any subscription. But keep in mind that resource guard only works if the users that should not have the permissions do not have permissions on the resource guard resource. That is why the resource guard resource is usually in another subscription to prevent users who have access to the vault does not have access to the resource guard resource.
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