This doesn’t really apply if you’re port forwarding to a specific device. In that case you know that you have told your firewall to forward port 80 & 443 (for example) to your web server and you know what ports that has open. I would not be using UPNP on the other hand as that seems dangerous especially in the IOT era.

Keep in mind you can always use a different DNS provider who does support dynamic dns. For example you could use cloudflare (free) with a domain bought from Pork Bun.