difference between nginx and ddns service

[Drake97]

Hello everyone,

As the title says, I wanted to ask you what is the notable difference between using nginx and a ddns service, beyond perhaps security.
Currently I have a ddns service (NO-IP) which is enabled with the port of jellyfin and from the outside I can enter as MyDDNS.bla.bla:PORT and everything work flawless, but I feel that perhaps being a very specific service in addition to my port is "visible", it is not as secure as it seems or maybe I'm wrong.
What do I gain in general terms if I use nginx instead of my DDNS service? it is worth mentioning that I have a dynamic public ip with my isp and that is the reason why I use a DDNS service.

If nginx is something better, how is the best way to install and configure it? as much as I read the networking section in the documentation I feel that I do not understand, or I am misunderstanding the details.

Thanks in advance