I use Linux Mint myself. The last time I installed an addon / plugin in FreeCad, I did it from within FreeCad itself: FreeCAD / Tools / Addon Manager / Workbenches (pull down box) and then start with the Refresh local cache and Check for updates buttons at the bottom of the window.
Alright, I figured. Both files .gitconfig and .gitignore were symlinks. So I copied the actual source files and the installation via the AddOn manager worked!
Thanks for helping me in the process of rubber ducky