https://news.ycombinator.com/item?id=40270219
Not sure what you mean by source/platforms, you might find what you need for your operating system on that discussion 3 weeks ago with links to options for macOS, Linux, and Windows.
https://vb-audio.com/Cable/index.htm
So, if you wanted to transcribe the audio from one of your physical output devices (say you had your meeting software outputting on external headphones), you could set the virtual audio device as the monitoring device on the physical external headphones. Therefore, you end up with a virtual audio input device containing the audio from your meeting software. I also do this to apply a chain of filters to my condenser mic in OBS because it picks up everything.