Sims 3 64 bit won't launch on macOS Big Sur

@wilmahagstrom  Unfortunately, your particular model of laptop does have some trouble running Sims 3.  One thing that can help is turning down the lighting and trees graphics settings to the minimum.  Do so at the Main Menu and quit to desktop before loading a save.  If that doesn't make a difference, try disabling Advanced Rendering (it'll make some things look pretty bad, but this is just a test) and enabling object hiding, if it's not enabled already.

Please test in Sunset Valley; Bridgeport has some issues related to how it's built, and that can complicate testing, especially when pets are involved.  I'm not saying you can't play in Bridgeport, only that it's best to get the game to a stable point in SV first so you can distinguish between different types of issues.

If turning down the graphics settings doesn't help, try uninstalling Pets.  You can do that by simply removing the folder for it, which is labeled EP05 and is in the same place as the Sims 3.app, either in Applications > The Sims 3 Packs or Users > your username > Applications > The Sims 3 Packs.  You'll need to start a new save to test this, as your existing saves would either not open at all or be corrupted by the missing data.