@wing, I’ve done much the same thing, though I use screen capture for the images. With screen capture, I could show the video editor program, but in my case, I don’t want to do that. I hadn’t thought of exporting PDF, so thanks for the idea. 
I’ve just figured out how to capture Dorico audio in recording apps such as Camtasia and streaming platforms such as Zoom, which I posted about here, so I no longer have to export the audio and pull it into Camtasia. If I could get that playhead to disappear, I wouldn’t have to create those images and bring them into Camtasia.
Honestly, it’s not the end of the world if we can’t get the playhead to disappear, but it would save some time when making videos of Dorico in Edit mode where I don’t want the playhead visible.