@lundquist02 Catalina did and does support the 64-bit version of Sims 3; it just doesn't run the 32-bit version. The same is true of Big Sur.
The error you're seeing is what happens when someone tries to download the 32-bit version of Sims 3 in an OS that won't run it. Please make sure you're downloading the correct version, both for the base game and for your pack.
If the 64-bit version isn't in your Origin library, or Pets isn't showing as owned specifically in the 64-bit version, you'll need to contact EA customer support and ask that the entitlement(s) be added to your account. Please see this thread for more information:
