GothBae In case it's not clear, there are always two Sims 4 folders, one with the game's program files (what the EA App installs) and one with the user data (saves, mods, etc.). And these two folders should never be combined.
Please post a screenshot of the error you're getting when trying to move the Sims 4 folder, and let me know where it's currently located and where you want it to be.
Please also keep in mind that you'll need to create a symbolic link after moving the folder so the game knows where to look for your data. Here's how:
https://crinrict.com/blog/2020/02/moving-windows-documents-folder-to-external-drive-via-symbolic-link.html
But that's a moot point until you can actually move the folder.