Reproduction steps:
1. Open the user’s attached project
2. Open Assets/Scenes/SampleScene
3. Open Window -> General -> Game
4. In Hierarchy window select Decal and set its layer to UI
5. Select Main Camera and in Camera component in section Rendering -> Culling Mask deselect Default
Expected result: The Decal is rendered
Actual result: The Decal is not rendered
Reproducible on: 12.1.7 (2021.3.8f1), 13.1.8 (2022.1.13f1), 14.0.3 (2022.2.0b4), 15.0.0 (2023.1.0a5)
Couldn’t test on: 10.10.0 (2020.3.38f1) - No Decal render feature
Reproducible with: macOS 12.5