How to reproduce:
1. Create a new Unity project
2. In the Assets folder, create a new UI Document
3. Open it in UI Builder
4. In the UI Builder Hierarchy, add a TextField and select it
5. Navigate to Attributes → Language Direction and set it to RTL
6. Navigate to Text → Advanced Text Settings → Text Generator Type and set it to Advanced
7. In the Viewport, enable the Preview mode
8. In the TextField input some text
9. Try to delete the inputted text using the Backspace key
10. Observe the Viewport

Actual result: No text is deleted
Expected result: The text is deleted

Reproducible with: 6000.3.8f1, 6000.4.0a1 (b27b8eafe426), 6000.4.0b8, 6000.5.0a6
Could not test with: 2023.1.0a1, 6000.0.67f1 (The Advanced Text Generator Type was introduced in Unity version 6000.4.0a1)

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

Notes:
- Using the Backspace key, it is possible to delete characters except for the first and last one, but it deletes them to the left instead of to the right
- Trying to delete characters using the Delete key also does not work as intended; it deletes characters as it should, but if you delete the last one, then after that character is deleted, the cursor jumps back to the front