If you’re a Comcast customer, note that Comcast will automatically block dns.nextdns.io.
To enable, you need to download the Xfinity app and disable Advanced Security.
In the Xfinity app go to: Overview > View Network Details > Advanced Secuirty > Disable . Next, go to my.nextdns.io and under Setup Guide click Browsers and follow the instructions for your browser. Make sure you identify your device. You need to URL encode a device name (of your choosing) to the end of your DNS-over-HTTPS endpoint. The example the nextdns guide gives goes as follows:
2. Append the name to the provided URL (the name should be URL encoded).
3. For “John’s Firefox”, you would use https://dns.nextdns.io/fca3b8/John's%20Firefox as your DNS-over-HTTPS endpoint.
Your browser will then be able to resolve handshake domains properly.