Jittery collisions in Unity 2D

I tried to implement a simple movement to my object. My object moves perfectly fine but I’m having issues with its collision. When I keep on moving object towards the obstacle/ground, collision are jittery.

Here the code for what I’ve written.

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

public class TempScript : MonoBehaviour
    (SerializeField) float walk_speed = 5f;
    (SerializeField) float jump_speed = 10f;
    (SerializeField) float max_up = 7f;
    (SerializeField) float max_low = -1.5f;
    void Update()


    void PlayerMovement()
        if (Input.GetKey(KeyCode.W) && transform.position.y <= max_up)
            transform.position = transform.position + Vector3.up * jump_speed * Time.deltaTime;

        if (Input.GetKey(KeyCode.S) && transform.position.y >= max_low)
            transform.position = transform.position + Vector3.down * jump_speed * Time.deltaTime;

        if (Input.GetKey(KeyCode.D))
            transform.position = transform.position + Vector3.right * walk_speed * Time.deltaTime;

        if (Input.GetKey(KeyCode.A))
            transform.position = transform.position + Vector3.left * walk_speed * Time.deltaTime;

The cube goes below the ground and bounces right back up.

The cube goes below the ground and bounces right back up. making it look like its jittering.
what i want is movement should stop when its colliding with object. just like it happens with addForce method.

for now you can ignore max_up and max_down variable, it was just to make sure its in the camera.