@peytonnelson Okay, let's try this. In either Applications or Users > your username > Applications, you should see a Sims 3.app, with a plumbob icon. In that location, do you also see a folder called "The Sims 3 Packs"? If so, please open it and let me know what's inside. If not, that means you don't have any packs installed.
To open the user Applications folder, open a Finder window, click Macintosh HD in the left panel, then choose Users > [your username] > Applications. If you don't see Macintosh HD, click Finder in the upper-left corner of your screen, then Preferences > Sidebar, and check the box next to hard disks.
If you do NOT have any packs installed, go back to your Origin game library, make sure to click on the 64-bit version of Sims 3, and scroll through the pack list looking for any Download buttons. Many of us see our packs listed two or three times, and only one listing for each actually works.
If you don't see a Download button for a particular pack, that means your account doesn't have the 64-bit "entitlement," as it's called, for that pack. In that case, you'll need to contact EA customer support and ask that the entitlement (specifically for the 64-bit version) be added to your account.
https://help.ea.com/en/contact-us/
If you prefer, you can instead contact EA Help on Twitter or Facebook.