You previously had to contact Steam customer support and ask for this, but there’s now a standard way you can delete games in a few clicks. When you remove a game from your Steam account, it’s permanently deleted. It’s just a way of sweeping a game under the rug for the moment. Someone can still see the game with a few clicks, and you can unhide the game in the future. When you hide a Steam game, it’s hidden from the standard library views. The Difference Between Hiding and Removing Games
