SoundFlower  is amazing Free and Open-Source extension to macOS BSD that allows you to create Virtual Audio Device in order to Route and Record Applications Audio. This is especially important for activities like Online Streaming and Presentation/Lectures Recording.
If you need more advanced Audio Routing with a nice GUI and lots of options try Loopback  from RogueAmoeba .
Thank you for this amazing fork and keeping it Open-Source! :-)