Thank you for the reply.
Yes, that clears up things for me.
The main reason I want to keep the tunnel closed is the 2 year meta-data retention laws we have here in Australia. They (the Politicians) promised us only the Government would use this data for reasons of crime and terrorism. But in the real world? This isn't the case, even local councils are, at times, accessing this data. I value my privacy.
However, when I do use Diversion with "policy rules strict" and Accept DNS Configuration set to "Strict". I connect to US ProtonVPN (or ExpressVPN) servers, and the DNS leaks (as we know). Then when I do try to watch US HULU, US Netflix, or US Prime Video I get proxy warnings. Without the DNS leaks I do not have this issue. However, with the DNS leak I can watch DirecTV in my browser, and CNN go etc
So, how I've resolved this issue was to take my ISP's Modem/Router out of Bridge Mode, setup it's WiFi, and I used a TP-Link Range extender at the back of the house for the Roku to connect to in order to access Australian content. Problem solved. No need to route anything else to the WAN.
But I'll still install Stubby and test it. I may need to use it, at times, at some time in the near future.
Edit: By the way, I like your website. It has some great articles.