New Input System

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.InputSystem;

//Obliga a que quien tenga la script agregada como componente requiera un rigidbody 2D (en este caso)
[RequireComponent(typeof(Rigidbody2D))] 

public class PlayerController : MonoBehaviour
{
    Rigidbody2D rb;

    public float speed;

    private float movementX;

    private float movementY;

    private void Start()
    {
        rb = GetComponent<Rigidbody2D>();
    }

    private void OnMove(InputValue movementValue)
    {
        Vector2 movementVector = movementValue.Get<Vector2>();
        movementX = movementVector.x;
        movementY = movementVector.y; 
    }

    private void FixedUpdate() 
    {
        rb.velocity = new Vector2(movementX, movementY) * speed;
    }
}

Muchísimas gracias, era justo lo que buscaba !!