We have just shipped an updated Steam Client to the Preview/Beta channel.
General
Added a setting to disable the screensaver when in game
Windows binaries registered as non-steam games will now run in Proton by default.
Fixed a case where non-steam games would fail to launch after changing the Target binary via the Browse button.
Fixed a case where the 'Stop' button would fail to close the game if it was launched by an external tool.
Fixed a case where library playtime could temporarily show an incorrect value.
Steam Input
Steam Controller Firmware