@hannahwhite99 Delete the five cache files in your Sims 3 game folder in Documents\Electronic Arts. They should be deleted regularly anyway, and while you're troubleshooting, delete them every time you quit the game. For reference, they are:
If that doesn't help, please test a new save and let me know whether it crashes.
Still crashing I deleted all of those files, it restarted the Mac whilst I was playing. Anything else I could do?
@hannahwhite99 Was that in a new save, or in your existing save? Please test, in Sunset Valley, Riverview, or Twinbrook, if you haven't already.
If the new save still crashes, please move your entire Sims 3 game folder out of Documents\Electronic Arts and onto your desktop. When you launch the game, a clean folder will be created with no content. Don't add anything to it yet, just test in Sunset Valley or Twinbrook (Riverview wouldn't be installed) and let me know what happens.
If you still get crashes in the clean folder, please make sure iCloud isn't set to automatically sync the contents of Documents. You can disable iCloud or just tell it not to sync; it's easy enough to manually back up your files to the cloud when you want.
https://bluebellflora.com/2017/02/06/sims-3-and-sims-4-not-loading-save-games/
If none of this helps, please list the specs of your Mac, as described here:
Please also list the packs you've installed.
