Re: I am having trouble creating a symbolic link
The mv command would not copy a file/folder, it would move it. cp is the copy command. Creating a symlink is not as easy as simply moving files around different locations which is why I strongly suggest that unless you're comfortable in Terminal, it isn't the solution for everyone.
If you've done it multiple times before then the issue will be in a command you have entered this last time. I wrote a guide here with full instructions https://bluebellflora.com/saving-your-sims-4-folder-to-an-external-drive/
