Cannot access addons externally (xxx.duckdns.org:PORT)

Thank you, that sounds more like it.
Thanks to your post, I found this one Using Nginx SSL Proxy to forward different domains to different services , which seems to be my case + your solution.

Reading that, I also realized that I have NGINX Home Assistant SSL proxy, and I have to switch to Nginx Proxy Manager. Do you agree? If that’s your case, would you mind sharing your config structure for the multiple domains with NGINX?

PS: I assume I have to create additional subdomains in duckdns too, right?

Thanks a lot again!