How to reproduce:
1. Open the “TerrainRepro“ project
2. Open the “ReproScene“ scene
3. Open the “Terrain (1)“ GameObject in the Inspector
4. In the Terrain Inspector click on the Paint Terrain icon
5. Select the Paint Texture tool
6. Add 5+ Terrain Layers
7. Click on the Terrain Settings icon
8. Under the Basic Terrain section set Cast Shadows to Shadows Only
9. Observe the Scene view

Expected result: The Terrain itself is not visible
Actual result: The Terrain itself is visible if the 5th or higher Terrain Layer is used

Reproducible with: 2021.3.43f1, 2022.3.45f1, 6000.0.18f1

Reproducible on: macOS 14.6.1 (Intel), Windows 11 (Reporters)
Not reproducible on: No other environments tested

Note: Not reproducible in the Game view or the Player