Compatibility Report

⁠Assassin's Creed: Black Flag Resynced (AppId: 3751950)⁠

System Information

Steam Machine 512GB (2026)

AMD GPU

Custom Steam Machine console configuration (Connected to a 4K Living Room TV).

Proton Version

Default selected stable Proton build, also tested on Proton Experimental & Proton Hotfix.

Game name

Assassin's Creed: Black Flag Resynced

Behavior

The native in-game HDR toggle refuses to stick. When toggling HDR to "On" in the video settings and hitting apply, the screen blanks out momentarily for a display handshake, but immediately returns with the setting reverted to "Off."

Note: The SteamOS Quick Access Menu (QAM) "Enable HDR" toggle works perfectly, triggering the expected system-level tonemapping pop, but the game engine itself fails to recognize native HDR availability.

Steps reproduced / Troubleshooting attempted:

1. Verified SteamOS QAM has HDR enabled.
2. Swapped between the game's available windowing modes (Borderless and Windowed).
3. Dropped the Steam client's "Maximum Game Resolution" properties from Global 4K down to 1920x1080 to prevent resolution-mismatched handshake drops.
4. Tested the environment variable flag in Launch Options: PROTON_ENABLE_HDMI_HDR=1 %command%
5. Appended the '-fullscreen' argument to the launch options to bypass borderless engine loops.
6. Forced the game to run via Proton Experimental.

In all scenarios, the behavior remains identical: the display blanks out and immediately reverts the native HDR toggle back to off.

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.