Attributes foldout is disabled for all elements when editing a UXML document in in-scene UI Authoring without being opened in UI Builder first

Steps to reproduce:

1. Create a new Unity project using the Universal 3D template
2. Right-click in the Hierarchy > UI Toolkit > Standard Elements > UI Library
3. Double click the "Multi Column List View" to add it and save the .uxml
4. Select the "Multi Column List View" in the Hierarchy
5. Observe the Attributes foldout in the Inspector

Actual results: The Attributes foldout properties are disabled for every element and no attribute value can be edited

Expected results: The Attributes foldout properties are enabled and attribute values can be edited

Reproducible with versions: 6000.7.0a4

Not reproducible with versions: 6000.6.0b7, 6000.7.0a3

Tested on (OS): Windows 11

Workaround: opening the same document in the UI Builder window enables the attribute fields, after which they are also editable in in-scene UI Authoring

Notes:

• Affects all element types, not just "Multi Column List View"