Sorry to clarify, Inside the pcb editor, there is a library manager that by default is pointing to github libraries, so an offline machine will never succesfully load them.
So to make it work offline requires going to the footprint library github pages, e.g.
And pressing download - download as zip file,
You then place the footprint libraries how you want, and add them to the library manager, and remove the github ones as you go,
There may be a cleaner way to accomplish it, but this is the one i am away of.