You can use the Screen Capture actor: https://troikatronix.com/add-ons/screen-capture/
Mini-Tutorial Video for the Screen Capture actor: https://www.youtube.com/watch?v=CQnDa6gslMg
For the reverse direction (streaming to YouTube from Isadora) you can use the RTMP Streamer actor: https://troikatronix.com/add-ons/rtmp-streamer/
Article for the RTMP Streamer actor: https://support.troikatronix.com/support/solutions/articles/13000089992-using-the-rtmp-streamer-actor/
Best wishes,
Woland