There's a tool called pkgutil, I was able to use this tool to unpack the pkg file (there is another one called xar but this one didn't work)
So by using pkgutil using an argument --extract-full instead of --extract (because --extract-ful isn't even displayed --help) I was able to extract the contents of the pkg file just like this:
pkgutil --expand-full <PATH_TO_PKG> <FOLDER_TO_EXTRACT_TO>
If you don't use the --expand-full option, the Payload folder won't have all the contents needed
So from there I ran the createinstallmedia using the --volume and --application path just to guess what! run into a new problem
It said that the macOS Sierra.app (which is a directory at all) was not a valid MacOS Installer file
Honestly, I thought this could be due to not using the standard installation methods that you usually do where it copies itself to the Applications directory
Unfortunately, this is a bug on the release itself. Bravo Apple. Love you, I don't understand how people blindly follow this company.
This guy explains the process (he exactly has the same release version as I do, from 2019. we are in 2023)
https://krieger.io/creating-bootable-macos-sierra-installation-media-on-macos-catalina/
Long story short: the InstallESD.dmg file is missing from the Contents/SharedSupport directory. So you have to copy it manually there. Then you have to change a version number from the Info.plist file.
Just impressive, this guy did a great work of reverse engineering.
This leads me to believe that resorting to a "friend" or "family" member to get this installed would have yielded the same results, as the issue was from the relase itself.
@P. Phillips. You are right, things chaned at Apple. To worse, no doubt. I am just impressed on how these older devices are no meant to repair, or reinstall
I have just managed to create the USB installer. Lets see which new problems arise (had to modify a few things on the release, so lets see to which new problems this leads me)