Reproduction steps:
1. Open the attached project
2. Double-click the "Doc" asset from the Project window to open it in the UI Builder window
3. In the StyleSheets Hierarchy section of the UI Builder window, expand Doc.uxml and select Element
4. In the Attributes Inspector section of the UI Builder Window, expand List
5. Using the "+" icon, try to add elements to the list
6. Observe the results

Expected result: Items are added to the list
Actual result: No items are added and the Console window displays an InvalidOperationException error message

Reproducible with: 6000.0.1f1
Couldn't test with: 2021.3.38f1, 2022.3.28f1 (UXMLObject attribute does not exist)

Reproducible on: Windows 11 Pro
Not reproducible on: No other environments tested