Computer sound sharing by panelists?

I've encountered sometimes-contradictory and seemingly often-legacy information on this topic.

Historically, the only way I was aware of to stream a video clip with an embedded audio track (an audio track that you wanted the audience to be able to hear) was for the moderator to in-advance upload it to GoToWebinar's server and then in-session temporarily switch from the then-active presenter panelist to it for playback, switching back to the presenter afterward.

Is it now possible in GoToWebinar (I'm not interested in GoToMeeting, etc.) for an active presenter to share not only his/her screen (application window or full display) but also computer sound, in order to (for example) be able to locally play back a video with an embedded audio track? And if so, is this still only a Windows-only panelist capability, or are MacOS panelist clients also supported? Thanks in advance for clarification!