Canvas Background foldout in UI Builder does not open/close when clicked on the title

Steps to reproduce:

1. Create a new Unity project using the Universal 3D template
2. Open the UI Builder window (Window > UI Toolkit > UI Builder)
3. Select the <unsaved file>.uxml in the Hierarchy tab
4. Click on the Canvas Background foldout's title
5. Observe the UI Builder window

Actual results: Nothing happens

Expected results: Canvas Background foldout opens/closes

Reproducible with versions: 6000.0.70f1, 6000.3.11f1, 6000.4.0f1, 6000.5.0a9

Tested on (OS): Ubuntu 24.04, MacOS Silicon Tahoe 26.3

Notes:

• Other foldouts in the same Inspector selection work as intended