ResourceDeploymentFailure when creating a HostPool for Azure Virtual Desktop

The host pool exists, but its managed session-host configuration reaches a failed terminal state. The displayed DeploymentFailed message is therefore a wrapper, not the underlying cause. Because you selected Create Session Host Configuration, Microsoft documents that diagnostics for this workflow are written to Azure Monitor and Log Analytics rather than the normal ARM deployment history. Enable host-pool diagnostics, retry once, and inspect the failure at that timestamp. Then verify the deployment identity has the required resource-group roles and can retrieve both Key Vault secrets; granting Key Vault Administrator only to your own account does not prove that. Also check regional vCPU quota, D2as v5 availability, subnet address capacity, and whether the selected 25H2 image supports Trusted Launch. Correct the first specific failure you find, then retry the configuration. If no detailed diagnostic record appears, open an Azure support case with the correlation ID.