[WORKAROUND] "An unknown error occurred" while downloading DLC on EA app for Mac

This just happened to me on my Mac, running Catalina 10.15.7 and I think somehow I got it to work?! When I went into the disk permission window again, I first added the actual Sims 4 game/app for full permission, which I selected from my external hard drive. Then in the same window, I searched for EA on my Mac and added full disk permission to the few that popped up: EAHelpLauncher and EABackgroundService. I restarted the EA app and then was immediately able to download the newest Kits I purchased! So maybe that could help you as well!