Remote Access to HA in Docker

Hello, I have an HA instance running in portainer on a RPi 4. I would like to remotely access it. I have, for other needs, a noip ddns and a VPN, so I can actually already do it. What I can’t do yet though is to integrate Google Home and Alexa.
I’ve seen some tutorials on how to gain external access, but they all refers to Supervised or OS and always using DuckDNS.
How can I use my already working ddns with my core installation?
Moreover, how secure is this kind of access in comparison to a VPN?