@a56cbd580cef3270 There are two approaches you can try here. The simple one is to create a new admin Windows account, a local one (so not linked to your Microsoft account), and work with that. The account will use default settings, including for the location of Documents, and the symlink command will work. You'll need to use that new account to play Sims 4, but you might just switch to using that account permanently, in which case I can show you how to transfer any files you want to keep to that account.
Your Sims 4 user data is already on the external, I take it, or at least it should be, so that part is fine. You'd launch the game once in the new account, delete the Sims 4 folder created in Documents > Electronic Arts, then use the symlink command to point to the correct folder on the external drive.
The other approach is to try to fix your main account. The command the print the location of Documents is just that: a command that says "provide this information." You can access it manually instead. Hit Windows key-R and enter "regedit" without quotes. Then open this location:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders
Look for the Personal entry, and post the value. It should look like a file path, e.g. C:\Users\etc., or say %USERPROFILE%\Documents.
The reason I need this information is that the symlink command can be tailored to whatever this value is, but I need to know what it is. Or if it's a location that will cause more problems, it should be changed first. If the value isn't there at all, please let me know; that brings up other possibilities that should also be addressed.