Reproduction steps:
1. Open the attached project “TextureProject”
2. Open the “Assets/New Scene.unity” scene
3. Select the “Assets/Texture.png” in the Project Window
4. In the Inspector Window, observe the Texture size in the thumbnail preview
5. Change the Texture Shape to “3D/2D Array”
6. Observe the new Texture size in the thumbnail preview
Expected result: Texture2D file size is 3.0MB
Actual result: Texture2D file size is 7.0MB
Reproducible with: 2020.3.35f1, 2020.3.44f1, 2021.3.16f1, 2022.2.2f1, 2023.1.0a25
Not Reproducible with: 2020.3.34f1
Reproducible on: Intel macOS 13.0.1