Applies temporary host optimisations (CPU governor, I/O and process priority) for the game's lifetime, then restores them on exit. GameMode runs the game, so %command% is what it runs.
Proton-Deck
Feral GameModeAdded Jun 29, 2026Last checked Aug 21, 2026
Safe
-dx11Copy
Use the DirectX 11 renderer (Unreal Engine games)
Effect
Selects DX11 as the RHI. Ignored by builds without a DX11 path.
Display
UniversalAdded Jun 27, 2026Last checked Aug 21, 2026
Safe
-ResY=1080Copy
Set the window height in pixels (Unreal Engine games)
Effect
Takes its value with = and no space. Epic pairs it with -ResX and -windowed.
Example
-windowed -ResX=1920 -ResY=1080
Display
Unreal EngineAdded Aug 11, 2026Last checked Aug 21, 2026
Safe
-ResX=1920Copy
Set the window width in pixels (Unreal Engine games)
Effect
Takes its value with = and no space. Epic pairs it with -ResY and -windowed.
Example
-windowed -ResX=1920 -ResY=1080
Display
Unreal EngineAdded Aug 11, 2026Last checked Aug 21, 2026
Safe
mangohud %command%Copy
Show the MangoHud performance overlay (Linux)
Effect
Draws FPS, frame timing and CPU/GPU load over Vulkan and OpenGL games. MangoHud runs the game, so %command% is what it runs.
Proton-Deck
MangoHudAdded Jun 29, 2026Last checked Aug 21, 2026
Safe
-fullscreenCopy
Run in fullscreen mode (Unreal Engine and Source games)
Effect
Overrides a saved windowed preference. -full is the same option in Source.
Display
UniversalAdded Jun 27, 2026Last checked Aug 21, 2026
Safe
-dx12Copy
Use the DirectX 12 renderer (Unreal Engine games)
Effect
Selects DX12 as the RHI. Ignored by builds without a DX12 path.
Display
UniversalAdded Jun 27, 2026Last checked Aug 21, 2026
Safe
-windowedCopy
Run in windowed mode (Unreal Engine and Source games)
Effect
Unreal documents pairing it with an explicit resolution. In Source -window, -sw and -startwindowed are the same option.
On the General tab, find the Launch Options field.
Type or paste the option (e.g. -windowed) into the field. To use several at once, separate them with spaces (e.g. -windowed -novid).
Close Properties. Steam saves automatically, and the option applies next time you launch the game.
To remove one, reopen the same field and delete the text. Options are game-specific; an option that helps one game may do nothing (or misbehave) in another.
Worth knowing: a launch option can break a game's rendering, reset local settings, or trip anti-cheat in multiplayer. Read the description first, add one at a time, and treat anything rated above Safe as a deliberate experiment.
