A useful script that allows you to run the method ApplyInputValue continuously while pressing a button in the new Unity Input System

ContinuousInputHandler.cs

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


public abstract class ContinuousInputHandler<InputType> : MonoBehaviour
      where InputType : struct
{
    private InputType m_ReadValue;

    private Coroutine m_CurrentCoroutine;

    private bool m_ShouldStartOnEnable;

    private void OnEnable()
    {
        if (m_ShouldStartOnEnable)
        {
            m_CurrentCoroutine = StartCoroutine(c_UpdateFromInput());
            m_ShouldStartOnEnable = false;
        }
    }

    private void OnDisable()
    {
        StopCoroutineIfPossible();
    }

    public void OnActionTriggered(InputAction.CallbackContext _context)
    {
        m_ReadValue = _context.ReadValue<InputType>();

        switch (_context.phase)
        {
            case InputActionPhase.Started:
                StartCoroutineIfNeeded();
                break;
            case InputActionPhase.Canceled:
                StopCoroutineIfPossible();
                break;
        }
    }

    private IEnumerator c_UpdateFromInput()
    {
        while (true)
        {
            ApplyInputValue(m_ReadValue);
            yield return null;
        }
    }

    private void StartCoroutineIfNeeded()
    {
        if (!gameObject.activeInHierarchy)
        {
            m_ShouldStartOnEnable = true;
            return;
        }

        if (m_CurrentCoroutine == null)
        {
            m_CurrentCoroutine = StartCoroutine(c_UpdateFromInput());
        }
    }

    private void StopCoroutineIfPossible()
    {
        if (m_CurrentCoroutine != null)
        {
            StopCoroutine(m_CurrentCoroutine);
            m_CurrentCoroutine = null;
        }
    }

    protected abstract void ApplyInputValue(InputType _inputValue);
}