Hi MS Techie,
Unfortunately I'm not aware of a way to use graph query to list Azure policies.
Azure Resource Graph queries resources within the scope of your subscriptions and tenant. Built-in policies are defined at the Azure platform level and are not stored within individual subscriptions.
You're probably going to need to use powershell commands like:
az policy definition list --query "[].{name:name, displayName:displayName, category:metadata.category, policyType:policyType}" --output table
az policy set-definition list --query "[?metadata.category=='Monitoring'].{name:name, displayName:displayName, category:metadata.category, policyType:policyType}" --output table