@Gavin Chisholm Thank you for reaching out to Microsoft Q&A.
I understand that you have questions regarding Managed disk with SSE using PMKs and if you can use it Cross Tenant. You can export the file and use it for a VM in a different tenant as when you export it, the file is decrypted.
However, since PMKs are managed entirely by Azure, you cannot use the same PMK for the VM in the other tenant for security purposes. CMKs can be used for cross-tenant purposes since they can be uploaded anywhere, whereas you can't interact with the PMKs.
Here are details for cross-tenant CMKs in case you want to learn more- https://learn.microsoft.com/en-us/azure/storage/common/customer-managed-keys-configure-cross-tenant-existing-account?tabs=azure-portal
Hope this helps. Please let us know if you have any more questions and we will be glad to assist you further. Thank you!
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