Re: Sims 3 base game won't launch: 'Unknown Error Occurred'
@HannahLynn98 The reason you're still getting the unknown error is that a regular install, either a straight deletion or the kind done through the uninstaller that comes with TS3, doesn't remove the game's hidden library files. You'll need to uninstall the base game again and then manually clean out those files. Here's how:
https://bluebellflora.com/how-to-do-a-clean-uninstall-and-reinstall-on-a-mac/
Then install the base game only, and run the Super Patch (digital download version) to manually patch the game to 1.67. The launcher doesn't do a good job of patching on its own.
https://bluebellflora.com/sims-3-manual-super-patch-for-mac-1-67/
If you still get an unknown error at this point, let me know. Otherwise, you can start installing your packs. There are four that don't install correctly (Ambitions, Late Night, Fast Lane, and Outdoor Living), and they need two workarounds, applied together, to fix the problem. The first is simple: create an alias for each pack that doesn't already have one in Applications, alongside the alias for the base game.
https://bluebellflora.com/sims-3-packs-not-showing-as-installed/
The second fix is to copy a folder for each of those affected packs into the folder for your newest pack by the date EA released it. (So that would be Into the Future if you have it, otherwise you can look up the release order.) This video shows you exactly what to do:
If you have any questions or would like further explanations, please feel free to ask. It would be helpful to know which packs you're installing though, so I can describe the steps more specifically.