Hi Caroline,
Unfortunately, Users cannot use Azure Governance Policy to restrict deployments initiated through -Microsoft Copilot in Azure (preview).
When any deployment operation is triggered through any Copilot prompts - Guided or Quick deployments, it does not create the resource with any such property that can differentiate it with other non- copilot deployments. So, policy cannot be applied to restrict it.
The only option currently available is to limit the users/groups who can access Copilot and manage the resources through that.
Reference Article for controlling Access: https://learn.microsoft.com/en-us/azure/copilot/manage-access#manage-user-access-to-microsoft-copilot-in-azure
Copilot Capabilities:
https://learn.microsoft.com/en-us/azure/copilot/capabilities
https://learn.microsoft.com/en-us/azure/copilot/use-guided-deployments
Since Copilot is in Preview, I strongly recommend sharing this as product feedback to allow some options to detect the copilot-initiated deployment by "user prompts" and restrict it - https://feedback.azure.com/d365community/
Through some automatically appended tags for the copilot-initiated deployment resources.
More granular RBAC access to control the copilot-initiated deployments.