I wrote a good code for simple movement but it still lagging and flickering

HI I don't understand why simple movement need to lagging, even on powerful devices. The devices that I use: pc GeForce GTX 1050 Ti, iphone 12 pro, and vivo. It would be worse if I recorded it.

The codes are okay. But I don't know why lagging in a sudden and sprite flickering. Should the problem be in project setting ? This a simple movement code:

 using UnityEngine;
  
  
 public class chunk_controller : MonoBehaviour {
  
  
     public float move_speed;
  
  
     private Rigidbody2D rb;
     private Vector2 dir;
     private public bool disable_move;
  
  
     void Start() {
         get = this;
         disable_move = false;
         rb = GetComponent<Rigidbody2D>();
     }
  
  
     void FixedUpdate() {
         move_position_movment();
         delete_chunk();
     }
  
  
     private void move_position_movment() {
         rb.MovePosition(rb.position + Vector2.down *  move_speed * Time.deltaTime);
     }
  
  
     private void delete_chunk() {
         if(
             transform.position.y <= -20
         ) {
             Destroy(this.gameObject);
         }
     }
  
  
     private void edit_references() {
         move_speed = 8;
     }
  
  
 }

[1]: https://forum.unity.com/attachments/ezgif-3-1cc29e5b0f-gif.1046210/?temp_hash=e7a57247f8c54d1c49be7c8cc25b2c7c

Project settings image: https://forum.unity.com/attachments...6/?temp_hash=e7a57247f8c54d1c49be7c8cc25b2c7c

Camera settings image: https://forum.unity.com/attachments...9/?temp_hash=e7a57247f8c54d1c49be7c8cc25b2c7c

Rigidbody2D settings image: https://forum.unity.com/attachments...2/?temp_hash=e7a57247f8c54d1c49be7c8cc25b2c7c