Hi - could you confirm, are you trying to install Windows Admin Center on the Azure Stack HCI OS itself, or are you installing in a VM running on the HCI cluster?
As per here: https://learn.microsoft.com/en-us/windows-server/manage/windows-admin-center/plan/installation-options#installation-supported-operating-systems, you can only install WAC on Windows Server (Gateway) or Windows 10. Azure Stack HCI can be managed by WAC, but you can't install WAC on Azure Stack HCI directly.
Hope that helps!
Matt