Netstat shows only applications that are listening on ports, not firewall or port forwarding rules. You have only Applications listening on your IPv6, but not IPv4. Also you use key -p but from output it is not clear who listening on those ports.
If port is opened in Firewall and router is another question. You have to check following points:
- Set port forwarding on you router, e.g. 443 to 443 on IP of your NextcloudPI and 80 to 80 on IP of your NextcloudPI. Or any other ports that you like to use for access from the internet.
- Open Ports by your firewall on NextcloudPI.
- Configure application to listen on those ports.
How you access you NC? Please provide more info: basically, here is a good and
Not necessary, for IPv4 you can use this this nice no-ip updater script on your NextcloudPI server.
UPDATE: I found that basically this all is written in the Doku and is part of nextcloud PI: https://docs.nextcloudpi.com/en/how-to-access-from-outside-your-network/