thanks @juriaan - i definitely understand this is not top priority. Izzy users are generally interested in live realtime connectivity and spatial, physical interaction, rather than directly outputting recorded media content.
It took a while for me to understand the difference, because when I first started using it, I couldn't believe there wasn't a 'Record Out' function. Now I get it. And it's no surprise. There's a reason, as Mark reminds us, for the name of the software itself. It comes from dance performance culture. And it's fab.
But for me, the 'liveness' of Izzy also makes it a powerful media production tool where you can 'perform' editing actions live and use media to trigger events within the edit, as it is 'recorded'. It behaves differently from Max/Jitter, Touchdesigner, VDMX or AfterEffects, etc and it gives a different aesthetic. So recording out is more important for me than others. No problem.
The good news (update) is that i finally got midiStroke to work after @jandraka (many thanks!) suggested it months ago. Thanks also to you @juriaan for what i guess is the Windows equivalent in this thread..?
For some reason midiStroke wouldn't recognise Isadora Virtual Out, but suddenly it does. Maybe a Catalina update..? Probably my error. I don't have much Midi experience.
But now I can send keystroke combinations out from Izzy and start and stop Syphon Recorder automatically from within a scene. This is like a powerful upgrade for me. A happy ending. I hope it will continue to work. Thanks to those who have contributed to this enquiry. Hope this is useful @yellow ...