Sorry I meant in your browser. Yes dns does not point to ports.

You would have to use some sort of reverse proxy that is only accessible from internal networks

Just to clarify a bit further. You browser doesn't specify ports in the URL because HTTP and HTTPS have basically coopted the 80/443 ports. You could have a website running an HTTP server on another port like 3000. But then you'd need to specify the port in the URL since the browser - by default - is looking at 80/443 and not 3000.

You should be able to configure the port for your Jellyfin server. I'm not a Jellyfin user, but most applications allow you to pick a port to run it on. So you'll have to change the port to port 80 and then expose that port on your docker container in the docker-compose file.

Edit: actually now that I think about it... You could just point your local port 80 to the docker container port. I forget the port mapping schema but it's something like

ports:
  - 80:1234

You might have to flip the order of the ports. But basically that example above is trying to map port 80 to port 1234. If that fails, you might have port 80 being used by another application on your computer and you'd either have to shut that app down, pick a different port for that app or you're back to picking a different port for Jellyfin