I’m not a network buff but how I understand secure DNS is that an Internet Service Provider (ISP) can still see that you are making DNS requests.
However, they cannot see the content of the requests, because it’s been encrypted.
So your ISPs can detect that you are using another DNS services and see the IP addresses you are connecting to, they cannot however decipher the actual domain names or URLs you are accessing. As far as I understand it, I’m sure someone more technical will correct this if I’m wrong in my assumption.
So this helps add a layer of privacy to your online activities, as ISPs are unable to monitor or track your browsing habits based solely on DNS queries.
So in regard to a next step there’s not much else I think you can do with your Quad 9 DNS.
You could enable the more secured Quad 9 version 9.9.9.11. See the link here for the extra features that gives you. Quad 9 Service Addresses & Features
But I think if you are wanting to up your privacy more against say your ISP, you may want to look at a VPN.