The update to SteamOS 3.8.15 for the Steam Deck has been released for all users.

It fixes an issue preventing HDR from being enabled in Assassin’s Creed Black Flag Resynced, along with a performance degradation that could occur when composition was required (such as with FSR enabled), plus general security and stability improvements.

SteamOS 3.8.15 has just been released for all users with the following changes:

General

• Fixed an issue preventing enabling HDR in Assassin’s Creed Black Flag Resynced
• Fixed an issue that would result in degraded performance in some cases when composition was required (such as when having FSR enabled)
• Security and stability improvements

Source: Steam