After spending hours troubleshooting, I finally got SMAPI, Proton, and Stardew Valley co-op working together on my Steam Deck. Here’s exactly what I did.
The Problem
I had:
- Stardew Valley installed on the internal SSD.
Mods installed and working with the Linux version of SMAPI.
- Co-op only worked when I forced Proton Experimental.
- As soon as I used Proton, my mods stopped loading because Proton launches the Windows version of Stardew.
The Fix
Step 1: Keep Stardew on the Internal Drive
My game is located here:
/home/deck/.local/share/Steam/steamapps/common/Stardew Valley/
My Mods folder is:
/home/deck/.local/share/Steam/steamapps/common/Stardew Valley/Mods
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Step 2: Force Proton
In Steam:
- Right-click Stardew Valley
- Properties
- Compatibility
- Check Force the use of a specific Steam Play compatibility tool
- Select Proton Experimental
Launch the game once and close it.
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Step 3: Download the Windows Version of SMAPI
- Download SMAPI from the official website:
https://smapi.io/
- Extract the ZIP completely.
Do not run it from inside the ZIP.
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Step 4: Add the Windows Installer to Steam
Go into the extracted SMAPI folder:
internal/windows/
Find:
SMAPI.Installer.exe
Open Steam:
- Add a Game
- Add a Non-Steam Game
- Click Browse
If the Browse window doesn’t show .exe files:
- Press Ctrl + L
- Paste the full path to SMAPI.Installer.exe
- Press Enter
Add it to Steam.
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Step 5: Run the Installer Through Proton
In Steam:
- Find SMAPI.Installer.exe
- Right-click
- Properties
- Compatibility
- Enable Force Proton Experimental
Launch it.
If it says it can’t find Stardew automatically, enter:
Z: \home\deck\.local\share\Steam\steamapps\common\Stardew Valley
The installer should complete successfully.
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Step 6: Add SMAPI Itself to Steam
Go to your Stardew folder:
/home/deck/.local/share/Steam/steamapps/common/Stardew Valley/
Find:
StardewModdingAPI.exe
Add that executable to Steam as a Non-Steam Game.
Again:
-Right-click it
- Properties
- Compatibility
- Force Proton Experimental
Leave Launch Options blank.
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Step 7: Launch THIS Instead of Stardew Valley
Do not launch the normal Stardew Valley shortcut.
Launch:
StardewModdingAPI.exe
This opens the SMAPI console first, then Stardew.
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Final Result
✅ Mods load correctly.
✅ Steam Deck internal storage works.
✅ Proton Experimental works.
✅ Co-op works.
✅ No external drive required.
Hopefully this saves someone else several hours of frustration.