How to reproduce:
1. Open the “DecalReproCQA“ project
2. Open the “ReproScene“
3. Open the “Plane (Default, Receive decals)“ GameObject in the Inspector
4. Set the Rendering Layer Mask to “Default“ and “Receive decals“
5. Open the “Decal (Default)“ in the Inspector and set the Rendering Layer to “Default“
6. Open the “Decal (Receive decals)“ in the Inspector and set the Rendering Layer to “Receive decals“
7. Observe the Game/Scene view

Expected result: Both Decals show up on the “Plane (Default, Receive decals)“ GameObject
Actual result: “Decal (Receive decals)“ does not show up on the “Plane (Default, Receive decals)“ GameObject

Reproducible with: 2023.3.0a18, 6000.0.16f1
Not reproducible with: 2022.3.43f1, 2023.3.0a17
Could not test with: 2021.3.43f1 (No Rendering Layers)

Reproducible on: macOS 14.5 (Intel)
Not reproducible on: No other environments tested

Workaround: Add another Rendering Layer in the Project settings