kaimelea I've moved your post to the master thread for the launcher crashing when opening the Downloads tab. It's not fixable on current versions of macOS. You can still install Store content through the Downloads Dashboard at the Main Menu... that is if you can login there, which it sounds like you can't.
What happens when you try to login? If you're getting stuck connecting, you can get unstuck by opening Keychain Access, in Applications > Utilities, searching for sims3 , and clearing the associated entries.
I would also clear Safari's cache and cookies, and also delete the file labeled [your email].bin in Documents > Electronic Arts > The Sims 3.
It was getting stuck connecting and clearing the "Keychain Access" entries allowed me to log in and download the worlds! THANK YOU!
