I entered a subdomain from DuckDNS in the local DNS records. My subdomain is Great-Wall.DuckDns.org. I can enter this domain in the url of my browser in the Pi-hole host and access the web interface. However, no other devices in my network can't. Strangely, I was able to access great-wall.duckdns.org once from a client PC but that was it.
Actual Behaviour:
Only host can access the web interface through great-wall.duckdns.org, all others have to use 192.168.1.2 without https.
Duck DNS links a fixed domain name to a periodically changing external IP, usually the "WAN address" of a home router. This can then be used to access home services that are being made externally available. It uses a script or a utility to link the current IP to the domain name.
Therefore there is no need to add your Duck DNS domain name to your Pi-hole. The Duck DNS service is responsible for keeping it up to date. Remove the entry from Pi-hole and then test again from outside your network.
Note – please don't make your Pi-hole itself available to the outside world. It will be found and abused very quickly. If you want to remotely access your Pi-hole you can keep using Duck DNS to locate your home IP, and set up a VPN for the DNS. There are guides available for WireGuard and OpenVPN, two popular free solutions.
