How to reproduce:
1. Open the attached “IN-135459” project
2. In the Project tab, select the “GameSettings” asset
3. In the Inspector, click “+” to add a new element
4. Observe the Console

Actual result: A warning is thrown, the binding is not functioning
Expected result: No warning is thrown, the binding works the same as with List

Reproducible with: 2023.3.0a2, 6000.0.68f1, 6000.3.10f1, 6000.4.0b10, 6000.5.0a7
Couldn’t test with: 2023.2.0a6 (VisualElement does not contain definition for “dataSource”)

Reproducible on: macOS 26.3 (M1 Pro)
Not reproducible on: No other environments tested

Notes:
- When using List<> instead of CustomList<>, in “GameSettingsScriptableObject.cs” script, bindings work correctly
- Warning thrown: [UI Toolkit] Could not retrieve the value at path '[0].username' for source of type 'CustomList`1': the path from the source to the target is either invalid or contains a null value. (InspectorWindow)