GameWindow.GetFullScreenMode

Получить полноэкранный режим окна.

using UnityEngine;
using UnityEngine.Windowing;

public class FullScreenModeExample : MonoBehaviour
{
    void Start()
    {
        var window = GameWindow.Main;
        FullScreenMode mode = window.GetFullScreenMode();
        Debug.Log($"Fullscreen mode: {mode}");
    }
}