I have an initramfs script which knows half decription key and fetches the other half from internet.
My threat model is: I want to be able to dispose safely my drives, and if someone steals my NAS needs to connect it to a similar network of mine (same gateway and subnet) before I delete the second half of the key to get my data.
How frequently do you send these updates? Most of dynDNS provider rate limit the updates you can send, so it is possible that you send a bunch of useless updates when the IP didn’t change and the actual update that is required gets discarded because you hit the limit.
Do you log your script errors somewhere? Are you sure that the IP changes so frequently?
I know at least 3 European fiber providers which offers static IPs. For broadband always on connections IP changes should be pretty rare
I use https://mycorrhiza.wiki/. It is really lightweight and stores data in a git repo. So it is terribly easy to export and backup it. the only drawback is that it uses its own markdown dialect