This update is for the SteamOS Beta and Preview channels, and includes new features that are still being tested. You can opt into this in Settings > System > System Update Channel.
Known Issues - Beta
There is a known issue with degraded performance in some cases when composition is required (such as when having FSR enabled).
This issue is fixed in the latest SteamOS stable release (3.8.16). Affected users may wish to switch to the stable update channel while we work on bringing this fix to the beta channel.
General
Fixed an issue causing black screens in certain launchers, including Zenless Zone Zero and FINAL FANTASY XIV Online