Take this hammerspoon lua script:

https://github.com/andrewarrow/cutlass/blob/main/scripts/ham...

And you can now press one buttons to start a movie recording and a screen recording at the same time.

After you have talked and demo'd your screen save the files and run:

./cutlass fcp add-video ~/Documents/test1.mov -o demo.fcpxml

./cutlass fcp add-pip-video ~/Desktop/test1.mov --input demo.fcpxml -o demo.fcpxml

And it will make you a final cut pro xml file you can import to FCP and have a video like:

https://www.youtube.com/watch?v=dxQkM0Sszeo