Simple script to lock/unlock the cursor in Unity using an input. Requires the "new" Input System package to work.

CursorLocker.cs

using UnityEngine;
using UnityEngine.InputSystem;

public class CursorLocker : MonoBehaviour
{
    public InputAction lockCursorAction;

    private bool _cursorLocked;

    private void Start()
    {
        lockCursorAction.Enable();

        //Setting it to initial state
        _cursorLocked = Cursor.lockState == CursorLockMode.Locked;
    }

    private void OnEnable() => lockCursorAction.performed += OnActionPerformed;

    private void OnDisable() => lockCursorAction.performed -= OnActionPerformed;

    private void OnActionPerformed(InputAction.CallbackContext obj)
    {
        ToggleCursorMode(!_cursorLocked);
    }

    private void ToggleCursorMode(bool newValue)
    {
        _cursorLocked = newValue;
        
        Cursor.visible = !_cursorLocked; //hiding/revealing
        Cursor.lockState = _cursorLocked ? CursorLockMode.Locked : CursorLockMode.None; //locking/unlocking
    }
}