I’m new to Unity, but I’ve done some research on this question before I asked. When I click “build and run” in the Unity editor, it doesn’t seem to respect my Full Screen Mode settings. I’m on windows, and every time my game starts, it’s full screen, even though I picked “Windowed.” Am I doing something wrong here?
If you ever started it fullscreen you might have remnant settings. Hold down alt when it starts and change the settings in the resolution dialog there.
I recommend making your own preferences system which uses a file you have some control over though. The registry is hard to back up for the average user, while a file in a common location is stored even by built-in backup tools.