It’s one of the features I love about Njalla for domains the most.
You don’t even need a ddns service because they support updating through simple https calls.
So I have a super tiny script that basically checks the WAN IP through ipify, then checks that against the routers current WAN IP, and if they match it does nothing and ends, but if its different, it sends out a curl with the new IP. I have it running every few minutes in a cronjob. It’s actually technically my service with the most uptime according to healthchecks.io.