Would it be possible for me to make comments to other instances etc?
Solved: I can’t, it would only work with a public domain.
Wouldn’t you need a publically available IP? DuckDNS is only for dynamic IP’s that is public, yes?
Works with anything that can open ports. DuckDNS works by pinging their service from anywhere to update the target IP for the subdomain.
See: Anything that can open ports. NAT of any kind tends to not allow opening ports.