How to reproduce:
1. Create and open a new project
2. Create a Terrain and a Cube
3. Select the Terrain and open the “Paint Details“ tab in the Inspector
4. Make the Cube a Prefab
5. Add a new Detail Mesh in the lower part of the Inspector
6. Put the Cube as the detail
7. Observe the Inspector

Expected result: No warning is displayed
Actual result: An “Atlas uncompressed.“ warning is displayed

Reproducible in: 2021.3.47f1, 2022.3.55f1, 6000.0.32f1, 6000.1.0a9

Reproduced on: Windows 11 Pro (23H2)
Not reproduced on: No other environment tested

Notes:
- The Cube is not assigned any texture that might be uncompressed, it is a default material
- Reproducible in URP and HDRP projects
- The error reads “Atlas uncompressed. This can be caused by mismatched texture formats.“
- Discussions Thread link: https://discussions.unity.com/t/terrain-atlas-uncompressed-warning/950458/4