Unknown error occurred, MacBook 2012 Mid

@papphanna  You can try bypassing the launcher, to see whether it helps:

https://bluebellflora.com/sims-3-how-to-bypass-the-launcher-on-a-mac/

But even if it works, you're going to get the disc authorization failure error when you reach the Main Menu.  This is because Mojave, and al newer versions of macOS, don't authenticate Sims 3 discs.  To get around it, you'll need to uninstall Sims 3, manually remove the hidden library files that the uninstaller doesn't delete, and install the game through Origin.  Then you won't need a disc to play.

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

After installing through Origin, be sure to run the Super Patch (digital download version) to manually patch the game.

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