Danro/Assets/Scripts/UI/FullscreenToggle.cs

using UnityEngine;
using UnityEngine.InputSystem;

namespace RR.Common.UI
{
    public class FullscreenToggle : MonoBehaviour
    {
        [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.AfterSceneLoad)]
        private static void Bootstrap()
        {
            var go = new GameObject("FullscreenToggle");
            go.AddComponent<FullscreenToggle>();
            DontDestroyOnLoad(go);
        }

        private InputAction _action;
        private bool _ownsAction = false;

        private void OnEnable()
        {
            // 1) Пытаемся найти PlayerInput и экшен "Fullscreen" в его Asset
            var playerInput = FindAnyPlayerInput();
            var fromAsset = playerInput && playerInput.actions
                ? playerInput.actions.FindAction("Fullscreen", throwIfNotFound: false)
                : null;

            if (fromAsset != null)
            {
                _action = fromAsset;
                _action.performed += OnFullscreenPerformed;
                _action.Enable(); // на случай если был выключен
                _ownsAction = false;
            }
            else
            {
                // 2) Нет PlayerInput/экшена — создаём локальный InputAction целиком кодом
                _action = new InputAction(name: "Fullscreen", type: InputActionType.Button);
                _action.AddBinding("<Keyboard>/f11");

                // Alt+Enter (левый Alt)
                var comp1 = _action.AddCompositeBinding("OneModifier");
                comp1.With("modifier", "<Keyboard>/leftAlt");
                comp1.With("binding", "<Keyboard>/enter");

                // Alt+Enter (правый Alt)
                var comp2 = _action.AddCompositeBinding("OneModifier");
                comp2.With("modifier", "<Keyboard>/rightAlt");
                comp2.With("binding", "<Keyboard>/enter");

                _action.performed += OnFullscreenPerformed;
                _action.Enable();
                _ownsAction = true;
            }
        }

        private void OnDisable()
        {
            if (_action != null)
            {
                _action.performed -= OnFullscreenPerformed;
                if (_ownsAction) _action.Dispose();
                _action = null;
                _ownsAction = false;
            }
        }

        private static PlayerInput FindAnyPlayerInput()
        {
            return FindFirstObjectByType<PlayerInput>();
        }

        // Если используешь PlayerInput в режиме Send Messages, метод с тем же именем тоже сработает:
        // public void OnFullscreen(InputAction.CallbackContext ctx) { if (ctx.performed) Toggle(); }

        private void OnFullscreenPerformed(InputAction.CallbackContext ctx)
        {
            if (ctx.performed) Toggle();
        }

        public static void Toggle()
        {
            if (Application.platform == RuntimePlatform.WebGLPlayer) return;

            bool fs = !Screen.fullScreen;
            Screen.fullScreenMode = fs ? FullScreenMode.FullScreenWindow : FullScreenMode.Windowed;

            if (fs)
            {
                Screen.SetResolution(Display.main.systemWidth, Display.main.systemHeight, true);
                Screen.fullScreen = true;
            }
            else
            {
                int w = Mathf.RoundToInt(Display.main.systemWidth * 0.5f);
                int h = Mathf.RoundToInt(Display.main.systemHeight * 0.5f);
                Screen.fullScreen = false;
                Screen.SetResolution(w, h, false);
            }
        }
        public static void SetFullscreen(bool fullscreen)
        {
            if (Application.platform == RuntimePlatform.WebGLPlayer) return;

            if (fullscreen)
            {
                Screen.SetResolution(Display.main.systemWidth, Display.main.systemHeight, true);
                Screen.fullScreen = true;
            }
            else
            {
                int w = Mathf.RoundToInt(Display.main.systemWidth * 0.5f);
                int h = Mathf.RoundToInt(Display.main.systemHeight * 0.5f);
                Screen.fullScreen = false;
            }
        }
    }
}