FirstPersonCharacter itself does not have Blur component, but the GameObject that has it attached does:

    [SerializeField] FirstPersonController FPC; /// <summary>Your First Person Controller.</summary>
    /// Option 1.
    private Blur blur; /// <summary>Blur's Script.</summary>
    /// Option 2.
    [Serializefield] GameObject objWithPFCAndBlur; /// <summary>So you could get both components from this GameObject.</summary>
    
    void Awake()
    {
        blur = FPC.gameObject.GetComponent<Blur>();
        if(blur == null)
        { /// As a good practice, you should do null checkings, on cases like this.
             Debug.LogError("There was no Blur attached to GameObject");
        }
        else /// Continue...
    }


Maybe you had problems because Components (such as Rigidbodys, MonoBehaviours, Colliders, etc) can have Components attached (so you can use GetComponent<Component>() method), but what usually you do on inspector is attaching Components to a GameObject, which was the case, FPC does not have a Blur attached, as you can see on your GameObject's inspector.

Hope that solves your issue.