mannnnnuu dockhals JeanieJean1015 As a test, please move the entire Sims 3 folder out of Documents > Electronic Arts and onto your desktop. If it copies instead of moving, or you get an error when trying to move it, stop here and let me know.
Otherwise, open the launcher to spawn a clean folder, download one Store item, install it, and see whether it works, both whether the launcher behaves and whether the content shows up in-game. If everything looks fine, restart your computer and check both the launcher and game again, just to be sure.
If this doesn't help, please create a new admin account on your Mac, repair the game (EA App > Sims 3 > Manage > Repair) and do the above there. Don't link the account to your Apple ID (you can skip this step).
If this doesn't help either, please let me know whether you use a third-party antivirus or any kind of cleaner app. Something may be blocking Sims 3 or deleting essential files.