Steps to reproduce:

1. Create a new Unity project using a 3D Universal Template
2. Go to Preferences > New Hierarchy
3. Make sure "Use new Hierarchy window" is enabled
4. In the Hierarchy, create an Empty GameObject
5. Create a another empty GameObject as a child of previously created GameObject
6. Repeat 5th step until GameObjects names do not fit fully
7. Observe horizontal scrollbar is available for navigating in Hierarchy
8. Resize the Hierarchy window so that the GameObject names are fully visible without scrollbar
9. Resize Hierarchy window back to the original size
10. Observe the scrollbar

Actual results: The horizontal scrollbar does not scroll fully, leaving some GameObject names partially hidden and not fully visible

Expected results: The horizontal scrollbar allows scrolling far enough so that the full names of all GameObjects become visible

Reproducible with versions: 6000.3.5f1, 6000.4.0b6, 6000.5.0a5

Can’t test with versions: 6000.0.66f1 (Hierarchy V2 not available)

Tested on (OS): macOS 26.2 (M1)

Notes:
- Resetting the Layout provides similar results