I'm more or less beginning developer and I'm currently working on a 3D game project with third person view. When I implemented first ActionMap into my character controller, everything worked fine, PlayerControls object has been called inside the class with input callbacks and it was enough for walking, sprinting, jumping, etc. But when I created another ActionMap for actions(attack, gather, interact) and decided to move PlayerControls implementation into another, centralized script, everything crumbled down. Upon starting play mode in unity I get a NullRefrenceException in the OnEnable cycle in PlayerLocomotionInput. After adding some lines for debugging, I've figured out that Instance is null at the beginning of LocomotionInput OnEnable cycle, in addition, I don't see a DontDestroyOnLoad folder in the hierarchy during play mode. What I was trying to do, is to make a class InputManager, create a singleton to access objects of this class and create PlayerControls object that can be accessed elsewhere:

public class InputManagerScript : MonoBehaviour
{
    public static InputManagerScript Instance;

    public PlayerControls PlayerControls { get; private set; }


    private void Awake()
    {
        if (Instance != null && Instance != this)
        {
            Destroy(this.gameObject);
            return;
        }
        else
        {
            Instance = this;
            DontDestroyOnLoad(gameObject);
        }
    }

    private void OnEnable()
    {
        PlayerControls = new();
        PlayerControls.Enable();
    }

    private void OnDisable()
    {
        PlayerControls.Disable();
    }
}

And a code sample from the ActionMap input script:

public class PlayerLocomotionInput : MonoBehaviour, PlayerControls.IPlayerLocomotionMapActions
{
    #region Variables and fields
    #endregion

    private void OnEnable()
    {
        InputManagerScript.Instance.PlayerControls.PlayerLocomotionMap.Enable();
        InputManagerScript.Instance.PlayerControls.PlayerLocomotionMap.SetCallbacks(this);
    }

    private void OnDisable()
    {
        InputManagerScript.Instance.PlayerControls.PlayerLocomotionMap.Disable();
        InputManagerScript.Instance.PlayerControls.PlayerLocomotionMap.RemoveCallbacks(this);
    }