Steps to reproduce:

1. Create a new Unity project using the Universal 3D template
2. Right-click in Hierarchy > UI Toolkit > UI Document
3. In the Inspector, in UI Document Component, click on the preset icon (the sliders)
4. In the Preset window, click "Create New UI Document Preset..." and Save it
5. From the Project window, select the newly created preset
6. In the UI Document Component, click "New" to create a Source Asset
7. Observe the Console and the preset

Actual results: "MissingReferenceException: The object of type 'UnityEngine.UIElements.UIDocument' has been destroyed but you are still trying to access it." is thrown, and the created asset is not assigned

Expected results: no errors and the created asset is assigned to the "Source Asset" property

Reproducible with versions: 6000.4.0a2, 6000.4.0b4, 6000.5.0a4

Couldn't test with versions: 6000.0.65f1, 6000.3.4f1, 6000.4.0a1 (the "New" button does not exist)

Tested on (OS): Windows 11