How to reproduce:
1. Open attached project: IN-118358
2. In the Project window open “Test” folder
3. In the Project window right click and select Create → Scripting → Assembly Definition
4. In the Project window double click the “Test.uxml” file (UI builder window should open)
5. Select Label
6. In the Inspector window select Data Source as Type, then click “Select Type…“ and select “CreatingType.cs“ script and in the third Data Source Input Field select any possible string type
7. In the Project window delete your created Assembly Definition file
8. Observe the Console window

Expected result: After deleting the assembly definition file the UI builder .uxml file is also cleared from all references to that assembly definition file
Actual result: After deleting the assembly definition file .uxml references aren’t cleared and error is thrown “TypeLoadException: Could not load type '.CreatingType' from assembly 'NewAssembly'.“

Reproducible with: 2023.2.0b1, 6000.0.61f1, 6000.2.9f1, 6000.3.0b8, 6000.4.0a3
Could not test with: 2023.1.0f1 (Data source binding feature is missing)

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

Note: When you are done with 6 step, in the “Test.uxml.” file a line similar to this should appear “<ui:Label text="Label" data-source-tyDpe="CreatingType, NewAssembly" data-source-path="randomString" />”