Bug Report: Far Cry 4 (Steam) fails to launch via Proton on Linux - Silent hang / Deadlock during initialization

1. System Environment
   OS: Fedora Linux 43 (Workstation Edition)
   Kernel: 6.18.16-200.fc43.x86_64
   Desktop Environment / Display Server: KDE Plasma / Wayland
   CPU: Intel Core i5-1235U (10 Cores, 12 Threads - Hybrid P/E Architecture)
   GPU: NVIDIA GeForce RTX 2050 (Hybrid Graphics / PRIME Offload) 580.126.18
   RAM: 16 GB
   Proton Versions Tested: Proton Experimental (experimental-10.0-20260227), Proton 9.0, Proton 8.0
   Launcher: Steam (AppID: 298110) + Ubisoft Connect (latest version auto-installed via prefix)

2. Issue Description
   Far Cry 4 fails to launch completely on Linux via Steam/Proton. Upon clicking "Play", the Ubisoft Connect launcher initializes properly, connects to the network, and seemingly hands over the launch to the game. However, the game window never appears.
   The process FarCry4.exe remains running in the background indefinitely, consuming ~5.5% of CPU usage. The game sits in an Rs (Running) state but is caught in a deadlock. It fails to even reach the stage of generating the GamerProfile.xml file in the compatdata documents folder.
   Crucial Context: Far Cry 3, Watch Dogs 1 run nicely without any tweaking.

3. Logs and Diagnostic Findings
   Generating a log via PROTON_LOG=1 reveals the following behavior:

• Continuous, infinite spam of NtGetContextThread and EXCEPTION_SINGLE_STEP.
• The engine appears to suffer a threading deadlock (likely Job Manager struggling with the Intel Alder Lake Hybrid P/E core architecture, or VMProtect anti-tamper failing to parse the Proton environment/CPU topology).
• Proton's accessibility tool (xalia.exe) was observed attempting to hook into the game process, which might be triggering the game's anti-cheat/DRM protections, causing it to intentionally trap the main thread in an infinite loop.

1. Extensive Troubleshooting Steps Already Taken (None succeeded)

• Clean Installation: Completely deleted the prefix folder (compatdata/298110) and cleanly reinstalled the game.
• Steam Input & Overlays: Disabled Steam Input entirely. Disabled both Steam Overlay and Ubisoft Connect in-game overlays.
• USB Polling Fix: Applied WINEDLLOVERRIDES="wineusb.sys,winebus.sys=d" to prevent known winedevice.exe segmentation faults. (Improved background stability, but game still hangs).
• CPU Topology Masking (Addressing Intel Hybrid Core issues): * Applied WINE_CPU_TOPOLOGY=4:0,1,2,3 to force a symmetric quad-core environment. Used Linux scheduler taskset -c 0-3 to physically restrict the process.
• Synchronization Toggles: * Used PROTON_NO_FSYNC=1 PROTON_NO_ESYNC=1 to prevent deadlock states. (This merely changed the process state from Running R to Sleeping S, but still no graphical output).
• Xalia Isolation: Blocked Proton's accessibility hook via PROTON_XALIA=0, WINEDLLOVERRIDES="xalia.exe=d", and physically renaming the binary in the Proton files.
• Graphics & Windowing: * Forced NVIDIA GPU via __NV_PRIME_RENDER_OFFLOAD=1 __GLX_VENDOR_LIBRARY_NAME=nvidia.
• Manually created the directory structure and injected a GamerProfile.xml forcing WindowMode="2" (Borderless) to bypass potential Wayland fullscreen capture bugs.

1. Tested Launch Parameter Combinations
   Below are some of the exact launch arguments tested via Steam, all resulting in the exact same silent deadlock:

• Vanilla test (after clean install): PROTON_LOG=1 %command% -skipintro
• Core isolation & Overlay block: WINEDLLOVERRIDES="wineusb.sys,winebus.sys,gameoverlayrenderer,gameoverlayrenderer64=d" WINE_CPU_TOPOLOGY=4:0,1,2,3 %command%
• Maximum isolation: PROTON_XALIA=0 PROTON_NO_FSYNC=1 WINE_CPU_TOPOLOGY=4:0,1,2,3 WINEDLLOVERRIDES="wineusb.sys,winebus.sys,gameoverlayrenderer,gameoverlayrenderer64=d" %command%

Any assistance or an engine-level patch / Proton workaround would be highly appreciated.

FC4Logs.zip