I got a reply from Zoom support and turns out it's a small box on the lower left of the 'Basic' sharing screen that you click to also include internal computer sound in addition to screen and external mic sharing. Not sure how that relates to the Computer Sound selection on the 'Advanced' sharing screen. If the latter is for sharing only sound and nothing else, I don't know what's Advanced about that since in the Basic screen you get both, including stereo if desired.
I could do either, but speakers would interfere with the microphone, so I'll probably have music via internal computer sound, and voice via external microphone, alongside a screenshare.
I got a reply from Zoom support and turns out it's a small box on the lower left of the 'Basic' sharing screen that you click to also include internal computer sound in addition to screen and external mic sharing. Not sure how that relates to the Computer Sound selection on the 'Advanced' sharing screen. If the latter is for sharing only sound and nothing else, I don't know what's Advanced about that since in the Basic screen you get both, including stereo if desired.