Project Preview Theme Runtime dropdown in the Project Settings does not update when a new Default Runtime Theme file is created or a selected Default Runtime Theme file is deleted

Steps to reproduce:

1. Create a new Unity project using the Universal 3D template
2. Create a new Default Runtime Theme file (Assets > Create > UI Toolkit > Default Runtime Theme file)
3. Open the Project Settings window
4. Open the UI Toolkit tab in the Project Settings window
5. Click on the Runtime dropdown under the Project Preview Theme
6. Observe the Runtime dropdown
7. Repeat steps 2, 3, 4, 5, 6

Actual results: The newly created Default Runtime Theme file does not appear in the Runtime dropdown

Expected results: The newly created Default Runtime Theme file appears in the Runtime dropdown

Reproducible with versions: 6000.5.0a4

Not reproducible with versions: 6000.4.0b3, 6000.5.0a3

Can’t test with versions: 6000.0.65f1, 6000.3.3f1 (due to no Project Preview Theme in the Project Settings)

Tested on (OS): MacOS Silicon Tahoe 26.1

Notes:

• The Runtime dropdown also does not update when a Default Runtime Theme file is deleted, still showing it in the dropdown and is selectable until the project is restarted
• Restarting the project makes the new Default Runtime Theme files appear in the Runtime dropdown