Nextcloud Routerports

I want install nextcloud Aio as a Docker-container.
in the first step nextcloud alone. In the next step using reverse proxy and certifikates .
So, suppose Port 80 and 443 in your router-subnet are used by another applikation. Normally I had to open other ports for http and https , lets say 6080 or 6443. Is that a way for installation or not ? If certifikates were reqest it may necessary to use defined ports strictly . Am i right ?