Sims 3 Problem connecting to Server on Mac

@mg75535  There are a couple different approaches.  You could stick with the base game alone and apply this workaround for the license server error:

https://answers.ea.com/t5/Technical-Issues-Mac/Sims-3-quot-Important-Message-There-is-a-problem-connecting-to/m-p/8317259#M5856

Or you could install your packs.  If you own any that are not World Adventures or High-End Loft Stuff, the presence of that pack should fix the error on its own.

Sims 3 doesn't run at all on Catalina (10.15), but it does fine on all earlier operating systems, up to and including Mojave (10.14).  Starting with El Capitan (10.11), there are issues installing four of the packs (Ambitions, Late Night, Fast Lane, and Outdoor Living); a couple of extra steps are needed to get them working.  I can provide instructions, if you'd like to try installing on your new Mac.  But it would be easier to describe the process if I knew which packs you wanted to install.