I don’t mean to hijack, but just given the name of this thread, I thought I would throw in another experiment that you can do 100% within Shotcut.
Posy released this video recently for a technique he calls “Motion Extraction” which can be achieved with a very simple combination of color invert and opacity filters in shotcut. This is especially easy since shotcut form composite video from the tracks that have content overlapping in time.
I would post a video of my own using shotcut, but I think it would be more satisfying for everyone to just try it for themselves. It’s so easy!