As long as whatever firewall rules you’re using is capable of resolving FQDNs then I don’t see an advantage of doing this. Maybe in the off chance that your IP changes, someone else gets the old IP and exploits it before the DDNS setup has a chance to update. I think that’s really unlikely.
Edit: just to add to this, I do think static IPs are preferable to DDNS, just because it’s easier, but they also typically cost money.
To resolve whatever hostname you’ve setup for ddns