How do you suspend key presses if a bool value is true?

I am trying to make some grid based movement where the character moves one tile for every key press with this code:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class PlayerController : MonoBehaviour
 {
     private Vector3 targetPos;
     private float tileLength = 1.1f;
     private float speed = 5f;
     private bool isMoving;
     Rigidbody2D rb;
 
     // Start is called before the first frame update
     void Start()
     {
         rb = GetComponent<Rigidbody2D>();
     }
 
     // Update is called once per frame
     void Update()
     {
         if (!isMoving)
         {
             isMoving = true;
 
             if (Input.GetKeyDown(KeyCode.UpArrow))
             {
                 targetPos = new Vector3(transform.position.x, transform.position.y + tileLength, 0);
                 StartCoroutine(MovePlayer(targetPos, "up"));
             } else if (Input.GetKeyDown(KeyCode.DownArrow))
             {
                 targetPos = new Vector3(transform.position.x, transform.position.y - tileLength, 0);
                 StartCoroutine(MovePlayer(targetPos, "down"));
             } else if (Input.GetKeyDown(KeyCode.LeftArrow))
             {
                 targetPos = new Vector3(transform.position.x - tileLength, transform.position.y, 0);
                 StartCoroutine(MovePlayer(targetPos, "left"));
             } else if (Input.GetKeyDown(KeyCode.RightArrow))
             {
                 targetPos = new Vector3(transform.position.x + tileLength, transform.position.y, 0);
                 Debug.Log(isMoving);
                 StartCoroutine(MovePlayer(targetPos, "right"));
             }
 
             isMoving = false;
         }
     }
 
     private IEnumerator MovePlayer(Vector3 tPos, string direc)
     {
         switch (direc)
         {
             case "up":
                 while (transform.position.y < tPos.y)
                 {
                     rb.velocity = new Vector3(0, speed, 0);
                     yield return null;
                 }
 
                 break;
             case "down":
                 while (transform.position.y > tPos.y)
                 {
                     rb.velocity = new Vector3(0, -speed, 0);
                     yield return null;
                 }
 
                 break;
             case "left":
                 while (transform.position.x > tPos.x)
                 {
                     rb.velocity = new Vector3(-speed, 0, 0);
                     yield return null;
                 }
 
                 break;
             case "right":
                 while (transform.position.x < tPos.x)
                 {
                     rb.velocity = new Vector3(speed, 0, 0);
                     yield return null;
                 }
 
                 break;
         }
 
         rb.velocity = new Vector3(0, 0, 0);
         transform.position = tPos;
     }
 }

After a bit of testing I think what's happening is that the isMoving bool isn't getting set to true at the beginning of the loop if it was previously set to false. So basically it's just constantly set to false when I don't think it should be. It feels like there's some super simple solution to this problem that I just don't know, but I don't know where to look XD.
Any and all help is appreciated!!!