Re: The Sims 3 64 Bit not Launching
@Gegahex Bluebellflora's guide to a clean uninstall isn't outdated; it's for the 32-bit version of Sims 3.
Anyway, please uninstall the game through Origin (right-click, Uninstall), then do a clean uninstall of Origin itself:
https://bluebellflora.com/how-to-uninstall-origin-on-a-mac/
Create a a new admin user account on your Mac, and don't import any settings or sync with any of your existing accounts, including iCloud. Download a fresh copy of Origin in that user account, install Sims 3, and see whether you can play. If not, please let me know whether you're using a third-party antivirus or a cleaner app.