If it helps anyone to help me:
I am on Telstra NBN in Australia.
I have a NBN modem (Arris CM8200B) which is connected to my Amplifi mesh. I do not think I am able to access the modem config to put it in bridge mode (I think this gets disabled by the NBN/Telstra)
I have toggled UPNP
I have tried to set up port forwarding (I think I did it right)
Still no joy
I note that when I set up port forwarding I used the IP address that Roon tells me is the “Roon cor ID”.
Not sure if it’s relevant but that is not the same as the IP address I get when I go to whatsmyipaddress.com. Nor is it the same IP address that my Amplifi mesh says it has