@John_Dickinson I have a Deco system but am using a Plusnet Hub One and I have it working. I understand the Hub One is similar to your home hub (i.e. it can’t be put into bridge mode). If you are able to put your Deco into Access Point mode (via Advanced settings in the Deco App under Operation Mode) then you’ll be able to avoid Double/Multiple NAT. All you need do then is configure the home hub to look for your Roon core, which to be honest required no specific IT skills on my part.
I wrote about how to do that in another thread here: ARC Port forwarding issue (ASUS router) - #11 by Red_R