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.
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. It should work fine in Desktop Mode however.
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.