Hey Matiss!
So I'm glad that you found my explanation helpful. Here are two screenshots showing two different ways of setting up picture-in-picture displays. First, I've got a large talking head, plus the slide inset as a smaller graphic. My students let me know that this made it hard for them to see the points on the slide, so I'm not using that approach anymore. It could work if you had a looping video playing in the small inset or something where the viewer doesn't need to be able to read anything in the inset image. You could also make the inset image larger.
View attachment 36000
In the next screenshot, I am using the opposite setup where I have a large slide and a small talking head. I think this works out better for the viewer.
View attachment 36001
The key thing to notice here is the order of the objects in the Sources window. The only way to control the way the objects layer is by the order in which they appear in the Sources window.In the first screenshot, you can see the slide image is first, then the video capture device (webcam) is second. This puts the webcam image on top of the slide in the output.
In the second screenshot, the slide comes second, so it sits on top of the webcam image.