This could be great news for all. Today EA have made an update available for Origin which apparently addresses some of the Sims 3 stability and compatibility issues those with more recent Macs are experiencing. This could be great news for all those suffering with the graphics card issues on post-2013 Macs but I haven't had any confirmation yet. This update is only available through Origin so if you are playing the game from the disc you will need to register your product codes in Origin and download the game digitally. If you need help doing this please read this guide (bear in mind you still have to download Origin from the link below, NOT from the link in the help article). This update is currently NOT available through the download option on the Origin website so don't head over there to get it.
It should change your current version of Origin to 126.96.36.19959
If you already have Origin installed it may be a good idea to use EA's Origin reset tool on your current installation before installing this new one. It may also be a good idea to completely uninstall any current installation of the game you have on your Mac before trying this and re-download and reinstall. Remember to move your user data from Documents > Electronic Arts > The Sims 3 onto your desktop before uninstalling if you want to keep your Saves etc.
Please leave as much feedback as possible about your experience using this update, it helps so much