Forget about having to download the Azure Stack HCI ISO file and having to convert it to VHDX to use for Software Defined Networking (SDN) deployment, you can now directly download the Azure Stack HCI VHDX file from the Azure Stack HCI software download site: Azure Stack HCI Registration | Microsoft Azure. Once you fill in your details and click on Submit, you will see an option to download the Azure Stack HCI software. In the “Choose language” dropdown menu, select “English – VHDX” and click on “Download Azure Stack HCI” to download the VHDX file.
For context, SDN in Azure Stack HCI uses a VHDX file containing the Azure Stack HCI operating system (OS) as a source for creating the SDN infrastructure virtual machines (VMs). The version of the OS in your VHDX should match the version used by the Azure Stack HCI Hyper-V hosts. This VHDX file is used by all SDN infrastructure components (Network Controller, Software Load Balancer and Gateways).
Official documentation for this change can be found here: Deploy SDN using Windows Admin Center - Azure Stack HCI | Microsoft Learn
Thanks
Anirban