I was informed by tech support that vMix Call does not currently support the system audio when doing screen share, the reason being that the actual implementation of that kind of support in WebRTC can be problematic.

In my opinion this lack of audio screensharing functionality is regrettable and a serious omission in an otherwise sophisticated high-end platform specifically designed for the audio/video streaming community. I purchased the 4K version at a considerable expense for me with the anticipation that I could service my guests, who are largely in this community, with the ability to share A/V content, be they in YouTube, MP4, or some other form.

 
Is there some technical reason why you can't add the same check box functionality, available in the FREE Zoom screen share, to include audio with the video. Wouldn't that be possible through the same connection audio is transferring between host and guests? I can play a video with audio, and talk over it simultaneously.

 
Is the limitation in the browser? If it requires the guest specifying the audio source for screen shares, where only one can occur at a time, couldn't that be added to the other advanced settings? You could even program the mic and line outputs to switch automatically, at the guest's discretion, when the guest initiates an audio screen share, if such switching is necessary. If the guest prefers to narrate over a video-only screen share, that option could then be turned off.

 
This should be available out of the box for all versions that include vMix Call, be convenient and easy to use. vMix could even make a big fuss over this new, great improvement!