Mouse rotation only works if it's not focused on game in Unity

Question

I'm new to Unity, I am working on a 3D game and I have a weird bug that I cannot solve. I wasted my whole day trying fix this. I am making a flying game and you navigate where you are going with your mouse. The problem is, every movement is working except mouse rotation (looking around with mouse). But here's the funny thing, it works if you for example while in play mode press "Windows key" and your cursor appears and you move it around, now my spaceship is turning around and rotating, but as soon as I press back into the game, it stops working. It's a really weird bug that I really don't know how to solve it.

This is what I use for looking around:

private void Update()
    {
        Rotate();
    }
 private Vector2 lookInput, screenCenter, mouseDistance;
 
    private void Start()
    {
        screenCenter.x = Screen.width * .5f;
        screenCenter.y = Screen.height * .5f;
    }
private void Rotate()
    {
        lookInput.x = Input.mousePosition.x;
          lookInput.y = Input.mousePosition.y;
 
          mouseDistance.x = (lookInput.x - screenCenter.x) / screenCenter.x;
          mouseDistance.y = (lookInput.y - screenCenter.y) / screenCenter.y;
 

I've tried changing the script in many different ways but nothing seems to work. I tried Brackey's movement / rotation and it technically works in game but only rotates up and down but when I try to rotate to the sides it's blocking me from doing it, it gets to maybe -1 and blocks me returns me back to 0 in Y rotation.

This is Brackey's way:

public float mouseSensitivity = 100f;
public Transform player;
float xRotation = 0f;

private void Update()
    {
        Rotate();
    }
 private Vector2 lookInput, screenCenter, mouseDistance;
 
    private void Start()
    {
        Cursor.lockState = CursorLockMode.Locked;
    }
private void Rotate()
    {
        float mouseX = Input.GetAxis("Mouse X") * mouseSensitivity * Time.deltaTime;
        float mouseY = Input.GetAxis("Mouse Y") * mouseSensitivity * Time.deltaTime;

        xRotation -= mouseY;
        xRotation = Mathf.Clamp(xRotation, -360f, 360f);
        
        transform.localRotation = Quaternion.Euler(xRotation, 0, 0);
        player.Rotate(Vector3.up * mouseX);

Answer 1

I think the problem you are having here is that when the script is triggered you set it to:

 Cursor.lockState = CursorLockMode.Locked;

This is locking the mouse to the centre of the screen, this is why when you hit windows it works because then the mouse is not longer locked. A fix for this would be simply to take that line of code away.