Launcher crashes when I open the downloads tab in Sims 3

IzzyAnng​  The workaround is to use the Downloads Dashboard at the Main Menu.  This is not completely reliable, but most players who've tried it have managed to install their Store content eventually.  There's some discussion about the process earlier in the thread, if you're interested.  I would suggest starting with a fresh Downloads folder and installing only a few items at a time, one at a time when you're dealing with worlds or compilations.