The Unknown Error message is to be expected if you have installed any of Ambitions, Late Night, Fast Lane, or Outdoor Living. Certain files do not get copied to their proper destination, so you have to do so manually. You may also need to create an alias (in your Applications folder, next to the alias for the base game) for one of those packs.
https://answers.ea.com/t5/The-Sims-Mac/CURRENT-ISSUE-Sims-3-Unknown-Error-in-El-Capitan-Sierra-High/...
https://bluebellflora.com/sims-3-packs-not-showing-as-installed/
If you've only installed the base game, the error could be caused by a few different issues. It's good that you patched the game, although if you downloaded it from Origin you would need to use the digital download version of the Super Patch instead of the one for the region where you live. Other issues that crop up on macs are related to incompatible graphics cards and the fact that the last few versions of OS X are not supported by TS3.
https://bluebellflora.com/unknown-error-message-sims-3-base-game-only/
If you're still having trouble, please post your computer's specs here so that someone can give you more targeted advice.
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I don't work for EA. I'm just trying to help fellow players with their games.
