I have unfortunately not been able to figure out how to load controller configurations that I have shared to steam into games that weren’t the original game I made that controller config in. I click on the controller layout and it fails to load and reverts back to the layout I already had selected.
My recommendation (cobbled together from recommendations from others) for getting around this is adding the file manager "Dolphin" (steam deck already has it) as a non-steam game to steam as well as “Corehunt” (which you have to download from Discover, it is made by the same people that made CoreKeyboard). Or you can just use Dolphin and Corehunt in desktop mode.
https://flathub.org/apps/org.cubocore.CoreHunt
https://gitlab.com/cubocore/coreapps/corehunt
Before I start, if y'all have a better way feel free to chime in and show me the light :P.
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Go to the game you want to copy a controller layout into. Edit one of the default controller layouts, make a random change to it, rename the controller layout to a unique name like TARGET_game then export the file as a personal save (or a personal shareable save I can’t remember which).
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In Corehunt, search for the file, Corehunt should find the file fairly quickly (it is muchhhh faster, fuzzier and more thorough than the other file search programs I have used on the Steam Deck so far). Note the file path.
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If needed, also search the name of the controller layout you want to copy into the game (name that layout something you can search for easily too).
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Navigate to the file path for your controller layout you want to copy, click split view in dolphin and then open up the controller layout for the game you want to copy the controller layout into (that contains your “Target_game” file) and… drag and drop copy!
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Done! Now when you go to browse layouts for your new game, the layout from your old game will show up and be loadable.
Note… you can also look up your steam deck’s file path to controller layouts in a guide or documentation but the filepath is really annoying and one of the folder steps is your steam user-id… so I actually think this explanation is much more concise and easy to do. Just let Corehunt find the folder location for you and then pin it to Dolphin’s sidebar so you can quickly jump to it again.
Steam games should name themselves according to the name you have in Steam, but sometimes the folder name is a number (the steam game’s id number or something).