I stumbled upon a script to automatically update a DNS record at one.com with your current IP-address.

Here is the forum thread: https://forum.netgate.com/topic/124904/dynamic-dns-one-com

And here is a link to the, as of writing, current script: https://lugico.de/one_com_ddns.py

In case the original site goes down I also repost the script here, but please check the original site to see if a newer version is available.

The script requires python and the requests package

pip3 install requests