There are games (such as Oblivion, Command & Conquer 3 Tiberium Wars...) that require "Steamworks" to run properly on Linux. However, when you simply click "install", "Steamworks" is not installed.

To solve this problem, you need to search for "Steamworks" and install it manually, or install any game that automatically installs "Steamworks" (such as GTA San Andreas, for example).

This bug has existed for over a decade and has never been fixed. It is sometimes mentioned on ProtonDB.com.

Effect on these games:

*In Oblivion, without "Steaworks", the launcher starts, but the "Play" button stays disabled, so it is not possible to start the game.

*In "Command & Conquer 3 Tiberium Wars", without "Steamworks", the graphics are horrible, failing, making the game "unplayable".

My suggestion is that whenever the user enables the "Steam Play for all titles" option, "Steamworks" should be installed immediately and automatically, as is already the case with the "Proton" engine.