Character clips through ground for one frame and then back up,Character clips through ground for one frame and then back up, how do i fix this?

I have scoured the internet for a solution, tried changing the collision detection to continuous, increased linear drag, messed a bit with the code, but nothing apparently works! Everytime I jump and get a bit of speed, that is a random chance that my rectangle player will slightly clip through the ground for a sec and pop back up, and i have no idea why using System.Collections; using System.Collections.Generic; using UnityEngine;

 public class Jump : MonoBehaviour
 {
     [Range(1, 10)]
     public float jumpVelocity;
     bool jumpKey = false;
  
     void Update()
     {
         if (Input.GetButtonDown("Jump"))
         {
             jumpKey = true;
         }
     }
     private void FixedUpdate()
     {
         if (jumpKey)
         {
             GetComponent<Rigidbody2D>().velocity = Vector2.up * jumpVelocity;
             jumpKey = false;
         }
     }
 }

This is my code for the jumping, its just a really simple test game, i'm trying to get the basics down but this is getting on my nerves, and it is so small but SO ANNOYING that i can't focus on anything else

Idk if it matters, but all the platforms are just white squares with collision boxes in a 2d game