r58hgzkm6882 This command is creating the symlink itself. The "file already exists" error means there's already a file or folder in the location where the system is trying to create the symlink, so in this case there's a Sims 4 folder in Documents > Electronic Arts Rename this folder to get around the error.
However, you need to link this Sims 4 folder to another folder called "The Sims 4," not to another folder, as in, the symlink needs to match the folder it's pointing to. So either move the entire Sims 4 folder to D, or only create the symlink for the Mods folder, like this:
MKLINK /J "C:\Users\username\Documents\Electronic Arts\The Sims 4\Mods "D:\Back up\Mods"
You'll notice I referenced the folder on D as Mods rather than Mods July 2025. That renming is necessary, as described above. You'll also notice my command is a bit different than yours. Here's the guide we use:
https://crinrict.com/blog/2020/02/moving-windows-documents-folder-to-external-drive-via-symbolic-link.html