AMA: Azure Virtual Desktop for Azure Stack HCI

I´ve successfully deployed multiple nested AzS HCI 23H2 in a mature testlab but keep pulling my hair lately when deploying AVD - Everything works from the the same logical network using the same onprem AD (VM connected to AD and ARC installed) - just the AVD deployment stales at "CustomScriptExtension" with "Machine is not connected (Code: HCRP400)" - Tried all the steps @ https://learn.microsoft.com/en-us/azure/virtual-desktop/troubleshoot-vm-configuration but no joy - "Error: Azure Virtual Desktop Agent and Azure Virtual Desktop Agent Boot Loader are missing. C:\Windows\Temp\ScriptLog.log is also missing" is my state .... Any hints where to get additional insights what´s happening ? Thx in advance!