How to reproduce:
1. Download and open the attached project
2. Open ProjectSettings/ProjectSettings.asset in a text editor (note that "selectedPlatform : 0")
3. Open the Project Settings window in the Unity Editor
4. Open the Build Settings window, switch platform to iOS, and create a build
5. Open ProjectSettings/ProjectSettings.asset again in a text editor
Expected result: "selectedPlatform : 2" setting is serialized into a user-specific file
Actual result: "selectedPlatform : 2" setting is serialized into a project-specific file
Reproducible with: 2021.3.13f1, 2021.3.18f1, 2022.2.6f1, 2023.1.0b3, 2023.2.0a1
Not reproducible with: 2020.3, 2021.3.12f1
Change was introduced by fix for [Internal link]