Compatibility Report

• Name of the game: The Sims 4
• Steam AppID: 1222670

System Information

• GPU: AMD Custom GPU 0405 (Steam Deck)
• Video driver version: Mesa (RADV VANGOGH)
• Kernel version: 6.11.11-valve27-1-neptune
• Proton version: Proton Experimental (10.1000-200). Also tested: Proton 9.0, GE-Proton9-23, Proton 10.0

I confirm:

• [x] that I haven't found an existing compatibility report for this game.
• [x] that I have checked whether there are updates for my system available.

Symptoms

Any .ts4script file (script mod) placed in the Mods folder triggers this error on launch:

"Unable to start - Content can't be loaded because the below file appears to be corrupted or was not created properly. If this is a Mod, please remove it and try again."

This affects ALL .ts4script files regardless of source, including known-good mods updated for the current game version (1.121.372.1020). The files are valid ZIP archives containing Python 3.7 .pyc bytecode (verified externally).

What works:

• Game runs perfectly with zero script mods
• .package files (CC/custom content) load fine from the same Mods folder
• scriptmodsenabled = 1 and modsdisabled = 0 confirmed in Options.ini
• Resource.cfg is correct

What was tried (all failed):

• Multiple Proton versions (Experimental, 9.0, GE-Proton9-23, 10.0)
• Multiple Proton prefix rebuilds
• Game version downgrade to 1.120 (script mods loaded once, but DLC depot mismatch caused other issues)
• Deleting localthumbcache.package and all cache files before launch
• Placing .ts4script files in Mods root vs subfolders
• Removing fgmod d3dcompiler_47.dll
• Fresh mod downloads from multiple sources
• File permission changes (chmod 755)

Key observation: The game loaded successfully with script mods exactly ONE time after a fresh Steam file verification, then failed on every subsequent launch with the same corrupted error. This suggests the game writes state during/after the first run that then breaks script mod validation on subsequent launches under Proton.

This used to work on earlier game versions. The issue appeared around the 1.121 patch (February 2026).

Reproduction

1. Install The Sims 4 on Steam Deck
2. Launch once, enable mods and script mods in Game Options
3. Close game
4. Place any valid .ts4script file in the Mods folder
5. Launch the game
6. "Corrupted" error appears for the .ts4script file

On Windows, the same .ts4script files load without issues.