Boom!
That was it! Thanks @Rugby
For me there was no need to Enable Insecure Guest Access in Windows
I found this in a Microsoft article…
By enabling insecure guest logons, this setting reduces the security of Windows clients.
More information
This setting has no effect on SMB1 behavior. SMB1 continues to use guest access and guest fallback.
It also said
SMB1 is uninstalled by default in latest Windows 10 and Windows Server configurations.
I would NEVER have found that if you hadn’t pointed that out. I still have no idea what it means. I wonder if Roon support realise that this is causing issues?
Thanks for letting me know and sticking with it!