I'm experiencing the exact same issues.
When I click on 'open downloads dashboard' within the sims 3 menu, nothing happens. Basically, the purchase is useless and non-installable. I had to get a refund. I find it insane that EA is unable to help with issues related to content being sold on the EA app, that ultimately can only be installed via the sims 3 launcher - which is ancient at this point.
Why doesn't EA make DLC's installable straight via the EA app the way they do their games? It makes no sense that we buy the DLC's on the app but are forced to install them via the launcher, which isn't supported by the newer generation Macs.
This has really turned playing the sims 3 into an almost impossible experience, without even mentioning the constant crashing mid-game... :(
