How to reproduce:
1. Open the attached project “Skybox”
2. Open the “SampleScene” scene
3. In the Project window, from the Assets folder, drag and drop the “New Material” Skybox Material into the Scene View
4. Press Ctrl+Z to undo the action
5. Press Ctrl+S to save the Scene and relaunch the project
6. Observe the Scene View
Expected result: The Skybox Material is still applied to the Scene after it was saved, and after undoing the action, the Skybox is gone
Actual result: There is no Skybox Material in the Scene after saving and undoing the action didn’t change anything
Reproducible with: 2020.3.45f1, 2021.3.19f1, 2022.2.6f1, 2023.1.0b4, 2023.2.0a3
Reproducible on: Windows 11 Pro
Workaround: Apply any other changes to the Scene, this way when you save the Scene, the applied Skybox will be saved too