Nowadays : Use Oculus Link
Old Days:
Download a special apk for Virtual Desktop :
https://github.com/guygodin/VirtualDesktop
Use adb install or SideQuest application to install it over the Oculus Quest
Download & install the virutal desktop streamer
Follow Virtual Desktop instruction.
The official Virtual desktop steamVR feature has been removed by Oculus, but the developer left it over this special apk.
You probably need to buy Virtual Desktop from Oculus Quest store.