Ubuntu 18.04
Trying to enable Steam Play in Steam with pulseaudio disabled, Steam will crash.

With pulseaudio disabled:

• Settings > Steam Play
• Checking both: "Enable Steam Play For All Games" "Use this tool instead of game-specific selections from steam"
• Press "OK"

Steam crashes. When starting Steam again Steam Play is still unchecked, or disabled.

Starting Steam with pulseaudio enable

In Ubuntu, "pulseaudio -D" in terminal
Repeating same steps, Steam Play gets enabled.