Sims 3 "Unknown Error"

g683mj7omfm7  Please list the full specs of your Mac: everything under About This Mac including the operating system and except for the serial number.

Please also let me know if there's a reason you haven't updated to macOS Catalina (10.15) or newer.  A 2017 Mac certainly can run Catalina, and some newer OSs, and that would be the simplest approach here.  But if you'd rather stay on Mojave (10.14) or earlier for other reasons, I can still help get Sims 3 working.

To be clear, simply installing a newer OS won't fix the problem.  What it will do is give you access to the EA App and the 64-bit version of Sims 3, which doesn't trigger the unknown error.

I tried to update to a newer Os but it did not let me. I’m not the best with computers so maybe I am doing something wrong there. Here are the full specs of my mac - 

MacBook Pro (13 in 2017, Two Thunderbolt 3 ports) 

Processor 2.3 GHz Intel Core i5

Memory 8GB 2133 Mhz LDDR3 

startup disk - macintosh HD

graphics - intel iris plus graphics 640 1536 MB. 

i tried clicking system update and it says “No Updates Available” 

I was able to download/install the start pack, Late night and high end loft but I still cannot play the game. 

g683mj7omfm7  Please uninstall Sims 3 as described here:

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

Since you're willing, please update your OS to Catalina, Big Sur, Monterey, or Ventura whichever you prefer.  (Ventura is the newest OS that supports your model Mac.)  Here are links to the installers for all newer versions, plus brief instructions:

https://support.apple.com/en-us/102662

Once you've installed the OS of your choice, install the EA App:

https://www.ea.com/ea-app#downloads

This will automatically remove Origin.  Login to the App with your EA account details and download Sims 3 from there.  If you can't, let me know what happens when you try.