What you’re looking for is called Dynamic DNS. I use Cloudflare for my DNS (which feels a little like making a deal with the devil) and Cloudflare-DDNS to automatically update my DNS records when my WAN IP changes. Basically, the container checks the current WAN IP, checks the current Cloudflare DNS records, and pushes a change if they don’t match. It runs every few minutes, and then rests again until the next check. I’m sure other DNS providers have similar ways to set up DDNS.

It’s not a 100% foolproof thing, because your WAN IP changing will take a few minutes to update. But a few minutes of downtime is much better IMO, when the alternative is needing to manually VPN into my server (if the VPN even still works, since the WAN IP changed), and troubleshoot it every time the IP address changes.