Player's Movement not smooth

When my player jumps and lands on something it always shakes around like that. I tried using a collider and I don't see anything in the movement script that may cause this. any solutions?

Player Movement script:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class PlayerMovement : MonoBehaviour
 {
     public static int movespeed = 6;
     public Vector3 userDirection = Vector3.right;
 
     public Rigidbody rb;
 
     public bool isGrounded;
 
     Vector3 jumpMovement;
 
     bool jump = false;
 
     [SerializeField]
     float jumpHeight = 1.8f, jumpSpeed = 8f;
 
     void Start()
     {
         rb = GetComponent<Rigidbody>();    }
 
 
     void OnCollisionStay()
     {
         isGrounded = true;
     }
 
     public float fallMultiplier = 3.5f;
     public float lowJumpMultiplier = 2f;
 
 
     void Update()
     {
         //movement
         transform.Translate(userDirection * movespeed * Time.deltaTime);
 
         if (Input.GetButton("Jump") && !jump)
             StartCoroutine(Jump());
     }
 
 
     IEnumerator Jump()
     {
         float originalHeight = transform.position.y;
         float maxHeight = originalHeight + jumpHeight;
         jump = true;
         yield return null;
 
         while (transform.position.y < maxHeight)
         {
             transform.position += transform.up * Time.deltaTime * jumpSpeed;
             yield return null;
         }
 
         while (transform.position.y > originalHeight)
         {
             transform.position -= transform.up * Time.deltaTime * jumpSpeed;
             yield return null;
         }
 
         rb.useGravity = true;
         jump = false;
 
         yield return null;
 
     }
 }