I want to download my sims 4 onto the D:/ Drive

@ScxrletWxdow  There are always going to be two separate Sims 4 folders.  One contains the game's program files, what the EA App installs, and you can choose to install to a secondary drive if you want.  The second folder contains user data—saves, mods, etc.—and is always in Documents > Electronic Arts.

To move the second folder, you can move all of Documents to the other drive, or you can create a symbolic link to show the game where to look.  I would suggest the latter even if the secondary drive is internal, but if it's external, please do NOT move Documents to it.  (Windows could react badly if the external were ever unplugged or unrecognized.)  Here's how to create the symlink:

https://crinrict.com/blog/2020/02/moving-windows-documents-folder-to-external-drive-via-symbolic-link.html

If you have any trouble with this, please post a screenshot of the Command Prompt window showing the command you entered and the result.

Please also make sure that the location where you're redirecting your user folder is NOT the same as the location where Sims 4 is actually installed.  Mixing these folders is never a good idea and will only complicate things, and the game might not even start.

So in an attempt to transfer the game between drives, I accidentally reinstalled the sims core files into D:\illeg\Documents\Electronic Arts\The Sims 4 and combined them, now all the program/game files are in the same folder, and the game won't launch. I have the backup game file folder on my desktop. I have so far transferred documents, desktop & downloads to my D drive from my C drive. I am so confused. Where is each folder *supposed* to be located in the directory?

@Jesslockhart1225  These are the files and subfolders within the Sims 4 user folder, which is always in Documents > Electronic Arts:

https://sims4.crinrict.com/eng/2014/09/user-files-explained/

You can discard most of this data—the game will regenerate it as necessary.  The only important folders are saves andTray, and possibly Mods, Screenshots, and Recorded Videos.

The game's program files can be installed anywhere, but combining them with the user data leads to bad results, as you're seeing right now.  If you want the game on D, I'd suggest creating a new folder on D, for example Games, and choosing that when installing Sims 4.

For now, make copies of saves, Tray, and anything else you want to keep, then uninstall Sims 4 through the EA App and restart your computer.  Reinstall the game to wherever you want it, but not in Documents at all.  Then try to launch the game and confirm that it works before adding back your saves and other user content.