Steam games no longer in library but still take up space

This has been a known issue with Steam for sometime. Although, per the Steam Support forums, it seems the most popular method to troubleshoot this:

  1. Check your steamapps/common folder to make sure the directories of said removed games are actually gone
  2. Make sure you have updated your Windows Restore points, as they can take up a lot of room with all that unused game data being kept
  3. If space is still not freed, back up any non-SteamCloud user data + games that keep local saves, then reinstall Steam

For future reference, Steam Support Forums are always a great place to start for Steam related problems! :)

Edit: I noticed you said storage app, comment added for clarification...