How to reproduce:
1. Open the attached “IN-90504” project in Unity 2023.1.0a14 or below
2. Open the Project Time Settings (Edit > Project Settings > Time)
3. Note the value of the Fixed Timestep field
4. Upgrade the project by opening it with Unity 2023.1.0a23 or higher
5. Open the Project Time Settings (Edit > Project Settings > Time)
6. Observe the value of the Fixed Timestep field

Expected result: The value of the Fixed Timestep field remains the same after upgrading the project
Actual result: The value of the Fixed Timestep field resets to the default after upgrading the project

Reproducible in: 2023.1.0a23, 6000.0.31f1, 6000.1.0a8
Not reproducible in: 2021.3.47f1, 2022.3.54f1, 2023.1.0a14
Could not test with: 2023.1.0a15 to 2023.1.0a22 (Fixed Timestep field visual bug)

Reproducible on: Windows 10 (by User), Windows 11
Not reproducible on: No other environments tested

Notes:
- Unable to confirm the Fixed Timestep field's actual value (FAV) in versions 2023.1.0a15 to 2023.1.0a22 due to the field displaying as corrupted. In version 2023.1.0a23, the issue is already present
- When downgrading the project back to the original version, the Fixed Timestep field contains the custom value again