I like how the patch tool works in Photoshop, and I think it would be useful in GoodNotes too. I would use it to edit diagrams and remove parts, such as labels, that I do not want. Here is an example of how the patch tool works: https://www.youtube.com/watch?v=II4lfxoNrJ8
Even though the patch tool is commonly used to edit photographs, it can definitely be used for editing illustrations too. I have used the patch tool in Photoshop before, and I started seeing the need for it again as I was trying to prepare diagrams for GoodNotes. I feel that it would be very beneficial if GoodNotes offered some tools for editing image backgrounds.
Other tools that can also be useful for editing diagrams are the clone tool, as well as tools for removing the background by making it transparent.
Even though there are other apps that already perform these functions, it would be much faster to prepare photos for our notes if we had some basic image-editing features within GoodNotes.