Steam Launch Option
Steam gives users the option of entering some custom options to prepend or append to a game's launch. This can be set under the game properties in the "Launch Options" section. Usually this field is used to add Game Command Line Arguments to a game's launch, and these vary between games, game engines and so on.
In our case, this is used to launch native Linux games with SteamTinkerLaunch.
For using SteamTinkerLaunch with Windows/Proton games, you should use the Steam Compatibility Tool option.
SteamTinkerLaunch can be set as a launch option, meaning you do not have to force SteamTinkerLaunch as a compatibility tool or add it as a compatibility tool. Using SteamTinkerLaunch as a launch option is intended for use only with native Linux games. Though it may work with Proton games, this is not advised or supported. SteamTinkerLaunch offers the launch option for native Linux games because forcing SteamTinkerLaunch as a compatibility tool will download the Windows release of a game, and so offering a launch option means you can leverage SteamTinkerLaunch with native Linux games
To use SteamTinkerLaunch as a launch option, simply add steamtinkerlaunch %command% to your native Linux game's launch options.
If you are using multiple launch options, you can instead set these within SteamTinkerLaunch by setting Game Command Line Arguments from the Game Menu.
If you installed via ProtonUp-Qt, you may have to add the launch option with the path to its installation. The following should work: $HOME/stl/prefix/steamtinkerlaunch %command%.
On Steam Deck in Game Mode there may be issues using SteamTinkerLaunch as a launch option (#630). It should work fine in Desktop Mode however.
By default, SteamTinkerLaunch enables the Steam Linux Runtime if it is installed and available for all games including native Linux games, which is not the default behaviour when running without SteamTinkerLaunch.
For Windows games, Proton 5.13 and up are intended to be used with the Steam Linux Runtime. It checks the required version defined in its toolmanifest.vdf under require_app_id). On Steam Deck, Deck Verified Native Linux games will use the Steam Linux Runtime by default, but this is not the case on the Linux Desktop, where the default behaviour is to just launch the executable.
Using the Steam Linux Runtime by default is usually fine and can actually fixes compatibility with a significant number of native Linux games. But if you don't want to use the Steam Linux Runtime, or if it breaks compatibility with a specific game, you can disable it under the Game Menu.
The way newer versions of the Steam client appends its internal launch options to games (specifically Steam Linux Runtime options) means you are very likely to run into issues using the launch option for Proton games. You may be able to get around this by disabling the Steam Linux Runtime from the SteamTinkerLaunch Game Menu, but this is not guaranteed and you should use the compatibility tool option for Proton games.
The functionality between the Steam Launch Option and Compatibility Tool should be identical, so use the one that best fits your game.