Compatibility Report

• Name of the game with compatibility issues: MULTIPLE GAMES (The Saboteur, Vampire: The Masquerade – Swansong, Control, The Witcher 2)
• Steam AppID of the game: 24880, 1299510, 870780, 20920
• Issue Type: PROTON RUNTIME REGRESSION (Controller Enumeration)

System Information

• GPU: Intel Arc A770 (DG2) / Intel UHD 770 (iGPU)
• Driver/LLVM version: Mesa (i915 driver) on NixOS 26.11
• Kernel version: Linux 6.x (NixOS 26.11 Zokor)
• Distro: NixOS 26.11 (Zokor)
• Link to full system information report: Gist
• Proton version: Proton Experimental, GE-Proton 11-2, GE-Proton 11-3 (BROKEN); GE-Proton 11-1 (WORKS)

I confirm:

• [x] that I have verified the problem happens on Proton Experimental AND GE-Proton 11-2/11-3.
• [x] that this is a REGRESSION: Works perfectly in GE-Proton 11-1.
• [x] that this affects MULTIPLE GAMES, indicating a runtime issue, not a game-specific bug.
• [x] that I am NOT using the GE-Proton flatpak.

Symptoms (Controller Enumeration Failure)

The DualSense controller (wired USB) is completely invisible to games in Proton 11.2+ and Proton Experimental. This occurs in The Saboteur, VTM: Swansong, Control, and The Witcher 2.

1. Without PROTON_PREFER_SDL=1: Controller is not detected at all.
2. With PROTON_PREFER_SDL=1: Controller is still not detected, and additional RPC errors appear (error 1726).
3. Regression Confirmation: Switching to GE-Proton 11-1 immediately restores controller detection in all listed games.

Reproduction

1. Launch any of the affected games (e.g., Control, The Saboteur) on NixOS.
2. Select Proton Experimental or GE-Proton 11-2/11-3.
3. Connect DualSense via USB.
4. Result: Game launches, but controller input is completely dead. The game does not see the device.
5. Comparison: Switch to GE-Proton 11-1 -> Controller works immediately.

Critical Log Errors

When PROTON_PREFER_SDL=1 is used, the following error appears, suggesting a device notification failure:

err:service:device_notify_proc failed to get event, error 1726   

(Note: Audio issues in The Saboteur appear to be a secondary symptom of this enumeration failure and are not present in all affected titles.)

Related Issues

• This report supersedes #10021, which was closed as a duplicate of a game-specific issue.
• Upon further testing, this is confirmed to be a Proton Runtime Regression affecting multiple titles (The Saboteur, VTM: Swansong, Control, The Witcher 2), not a bug specific to The Saboteur.
• The regression is isolated to Proton 11.2+/Experimental (works in GE-Proton 11-1).