That app is different from the Quest version of Virtual Desktop. The steam version runs on a PC and lets you use your desktop while in VR (on a headset connected to the PC). The quest version runs on the quest (with a paired "streamer" app on the PC) and lets you wirelessly connect to your PC. While connected to your PC through the quest app you can not only view your desktop, but also can play any pc vr game.
The quest app is one of the popular ways to wirelessly connect to a PC and play PCVR experiences. Other ways include Oculus's offical Airlink, and a free open source app called ALVR. Personally, I find Virtual Desktop the best experience out of those, but I think many people prefer Airlink.
if you purchase the steam version instead of the oculus store version, you would need to find another method to connect your Quest to a PC.
What Doesn't Work?
Most apps downloaded through the Oculus Store because of entitlement errors (including Virtual Desktop :/ )