Since Game Packs are installed directly from the Origin Client, uninstalling add-on content is only possible by uninstalling The Sims 4. Once you re-install the game, you can pick and choose add-ons to install again.
To uninstall The Sims 4, right click the game in the Origin Client and select “Uninstall”. This also removes any additional add-ons and game packs you may have purchased for your game. Uninstalling the game this way should not delete any of your game files, however, Crinrict suggests backing up your Sims 4 Folder.
NOTE: DO NOT use non-official methods which suggest deleting folders in the File System. It has not been tested, is known to generate warnings, and can cause issues with your game. Completely uninstalling The Sims 4 is the only official and safe way to uninstall content at this time.
With the release of The Sims 4 Outdoor Retreat, many players were left scratching their heads when the game pack they purchased did not show up in Origin as an individual game. We don’t yet know how EA will handle Expansion and Stuff Packs, but here’s a quick guide to finding your purchased content.
When you purchase new content via Origin web or client, the game will be placed in the “More Details” section of the game. When viewing the details of the game, scroll down the page to install any additional Add-ons.