How to reproduce:
1. Open the attached “IN-120502_repro” project
2. Observe the Game window. Notice that the corners of the black area are rounded
3. In the Hierarchy tab, click on the “UIDocument” GameObject
4. In the Inspector, in the UI Document component open the “PanelSettings” asset
5. Set the Render Mode property to “World Space”
6. Observe the Game window

Expected result: The corners of the black area are rounded
Actual result: The corners of the black area are not rounded

Reproducible with: 6000.2.9f1, 6000.3.0b8, 6000.4.0a3
Could not test with: 2022.1.0a5, 6000.0.60f1 (61dfb374e36f), 6000.2.0a1 (No Render Mode property in the Panel Settings asset)

Reproducible on: macOS 15.3.2 (24D81) (M1 Max)
Not reproducible on: No other environments tested

Note: Reproducible in Player