king_Elliott414 Forget signing in at the Main Menu. You don't need to, and it doesn't always work correctly anyway. If the game keeps trying to connect, open Keychain Access, in Applications > Utilities, search for sims3 , and delete any associated entries. If that alone doesn't help, clear the EA App's cache:
https://help.ea.com/en-us/help/faq/clear-cache-to-fix-problems-with-your-games/
If there's a particular reason you want to use the sign-in, like you're hunting badges or playing with SimPort, you can try again to login after deleting the above data. If it doesn't work, repeat those steps and just skip the login for now.
I'm not sure what you mean when you say you play through Steam though. Steam only hosts the Windows version of Sims 3; this has always been the case. It won't even install the Mac version. Maybe you added Sims 3 as a non-Steam game in order to be able to launch it from the Steam interface?