That seem to be a problem with your setup!
The Pico 4 is NOT ONLY a standalone headset. It works perfectly with MSFS and of course with steam VR. I am using the pico 4 to play MSFS and other steam VR titles 
The connection is done via virtual desktop.
Make sure to use only wireless connection, the cabled connection does not work entirely. Make sure to have a connection speed of at least 800mbit/sec.