Object Selector becomes unresponsive when selecting root UI Document as Data Source for Add Binding in UI Builder

Steps to reproduce:

1. Create a new project using 3D URP template
2. Create a new UI Document (Assets > Create > UI Toolkit > UI Document)
3. Open the .uxml file in UI Builder
4. Add a Visual Element to the Hierarchy
5. In the Inspector, choose any property (e.g. Text > Size)
6. Click on the three dots to the left of the property and select "Add Binding"
7. In the "Data Source" property click on the object picker to select Scriptable Object
8. In the "Select Scriptable Object" window select the created UI Document
9. Observe a pop-up appears saying "Template not set."
10. Click "Ok" or "No" (no difference)
11. Try to select another item in the "Select Scriptable Object" window

Actual results: The window appears frozen, no selection can be made without closing and reopening it

Expected results: Unsupported assets should not be selectable as binding data sources, and the object picker should remain responsive after an invalid selection attempt (or close automatically like in previous versions)

Reproducible with versions: 6000.0.61f1, 6000.0.73f1, 6000.3.13f1, 6000.4.3f1, 6000.5.0b4, 6000.6.0a3

Not reproducible with versions: 6000.0.50f1

Tested on (OS): macOS 26.4, Ubuntu 24.04

Notes:

• Could not find the FAV due to inconsistent reproduction, each time downgrading/upgrading showed different results
• The regression only seems to be present on Ubuntu 24.04, since on macOS the issue still reproduced on not regressed versions
• On 6000.0 the pop-up prompt has just "Ok" option instead of "No" and "Ok", but the end result stays same