Panel.Pick was never intended to work with world space content. We can't fix the Panel.Pick method to accept flat coordinates in the original document's inverse-transformed space because of the way the documents set their transform matrix on their rootVisualElement, which effectively requires a 3-D world coordinate as the entry point. A single panel can host multiple documents with various 3-D transforms on them, which makes the notion of a 2-D "panel coordinate" generally invalid in world space.
We do plan on releasing new, better-adapted methods for world-space interactions, notably for picking, but these will come as a feature release and not a bug fix.
That being said, I found a workaround by playing around that will make Pick work in the provided repro project:
- Create a new GameObject with an empty UIDocument using the same PanelSettings
- Place the new document's transform at (0,0,0) with default rotation and scale.
- Put the original document as a child to the new one (creating a nested UIDocument).
- Make sure to choose Position=Absolute in the nested document's inspector.
- Enter play mode and click on the color bands. Observe the console.