Steps to reproduce:
1. Create new Unity project using Universal 3D Template
2. In Hierarchy create Dropdown Field object (Right-click > UI Toolkit > Standard Elements > Dropdown Field)
3. In “Open UI stage” pop-up press “Continue” and save UXML file
4. When all files are created, enter Play Mode
5. In Hierarchy (NewUXMLTemplate) window expand “DropdownField” element, so that “VisualElement” child is visible
6. Select “VisualElement” child
7. Observe the Console window
Actual results: “No script asset for TempSerializedData. Check that the definition is in a file of the same name.” warning is thrown in the Console window
Expected results: No warnings are thrown in the Console window
Reproducible with versions: 6000.6.0a7
Can’t test with versions: 6000.6.0a6 and lower (No such feature to create UI Elements in Hierarchy window)
Tested on (OS): macOS Tahoe 26.4.1 (M1)