Sims 3 Won't Launch: Unknown Error Occurred on Mac

@Lighttdark1  The instructions you found to move files around are necessary in many cases, but not yours.  In case you're curious, they apply whenever one of the problem packs—Ambitions, Late Night, Fast Lane, or Outdoor Living—is not your newest pack by the date EA released it.  But LN is your newest pack, so that step doesn't apply to you.

The one step you do need to complete is to create an alias for Late Night in Applications, alongside the alias for the base game.  High-End Loft Stuff should already have one.

https://bluebellflora.com/sims-3-packs-not-showing-as-installed/

If this alone doesn't help, you'll need to do a clean uninstall and start from scratch.  You can keep your existing saves, or even your entire game folder that contains them (the one in Documents), elsewhere, and put it back when you're done.  Sometimes the leftover library files can prevent you from launching the game going forward.

https://bluebellflora.com/how-to-do-a-clean-uninstall-and-reinstall-on-a-mac/

Once you've installed the base game, run the Super Patch (digital download version) to patch the game to 1.67.  The launcher doesn't do a thorough job of patching, and the Super Patch won't hurt.  In fact, even if creating an alias fixes the unknown error issue, it's still a good idea to run the patch.

https://bluebellflora.com/sims-3-manual-super-patch-for-mac-1-67/

And if Origin itself locks up or otherwise doesn't cooperate, you can run the reset tool for macs:

https://help.ea.com/en-us/help/origin/origin/how-to-reset-origin-on-mac/

P.S.  You don't need to launch TS3 through Origin; just use the alias you create for Late Night.  In fact, you could uninstall Origin entirely if you wanted, and your game would still run the same.