SteamOS 3.8.16 has just been released for all users.

Version 3.8.15 was only released yesterday - this update mainly fixes a bug from that previous version.

General

Reverted a change from 3.8.15 resulting in some titles showing a blank screen. The Assassin’s Creed Black Flag Resynced HDR fix will be available in Beta while the root cause is investigated.

Source: Steam