Screen.SetResolution immediately applies windowed resolution when switching from Fullscreen to Windowed mode

Reproduction steps:
1. Make sure no external monitors are connected and only one display is used for testing
2. Open the attached “Resolution Bug.zip” project
3. Build and Run the project (File > Build and Run)
4. In the Player, enable the “Fullscreen” checkbox (if not enabled by default)
5. In the resolutions dropdown, select the lowest available resolution in the list (e.g., 960x540 or 1280x800, depending on monitor)
6. Disable the “Fullscreen” checkbox
7. Observe the resolution of the Player

Expected result: The Player window retains the previous full-screen resolution and Screen.width/Screen.height reflect that (e.g. 960x540 or whatever was set in the 5th step)
Actual result: The Player window immediately switches to a different resolution (e.g. 1920x1080 or whatever the first windowed resolution option is)

Reproducible with: 6000.0.62f1, 6000.2.13f1, 6000.3.0f1, 6000.4.0a5, 6000.5.0a1

Reproducible on: Ubuntu 25.04
Not reproducible on: no other environment tested

Note:

• See Internal Notes for more context