I have recently done a research on how to add the port 8080/tcp in my system and list all the active ports in a text file called "zones.txt". I use a Linux Mint 20.1 XFCE system and I came across the apt-package named Uncomplicated Firewall. This package allows you to open ports on your system and makes them ready for use using ssh.
Here is a screenshot on how to progress with the procedures.
I am also attaching my GitHub gist which provides an detailed explanation on how to implement this in your system.