How am I supposed to make sure that the player can fall through the ground?

Using Rigidbody2D and colliders is one way it could be achieved

1.Your Player needs to have a RigidBody2D
2. If the player already has a RigidBody2D, then it seems like the Background(In the Tilemap) has a TileMapCollider2D If you remove it then the player should fall through…

Does it have something to do with my code?

using UnityEngine;

public class PlayerMovement : MonoBehaviour
{
[Header(“Movement Parameters”)]
[SerializeField] private float speed;
[SerializeField] private float jumpPower;

[Header("Coyote Time")]
[SerializeField] private float coyoteTime; //How much time the player can hang in the air before jumping
private float coyoteCounter; //How much time passed since the player ran off the edge

[Header("Multiple Jumps")]
[SerializeField] private int extraJumps;
private int jumpCounter;

[Header("Wall Jumping")]
[SerializeField] private float wallJumpX; //Horizontal wall jump force
[SerializeField] private float wallJumpY; //Vertical wall jump force

[Header("Layers")]
[SerializeField] private LayerMask groundLayer;
[SerializeField] private LayerMask wallLayer;

[Header("Sounds")]
[SerializeField] private AudioClip jumpSound;

private Rigidbody2D body;
private Animator anim;
private BoxCollider2D boxCollider;
private float wallJumpCooldown;
private float horizontalInput;

private void Awake()
{
    //Grab references for rigidbody and animator from object
    body = GetComponent<Rigidbody2D>();
    anim = GetComponent<Animator>();
    boxCollider = GetComponent<BoxCollider2D>();
}

private void Update()
{
    horizontalInput = Input.GetAxis("Horizontal");

    //Flip player when moving left-right
    if (horizontalInput > 0.01f)
        transform.localScale = Vector3.one;
    else if (horizontalInput < -0.01f)
        transform.localScale = new Vector3(-1, 1, 1);

    //Set animator parameters
    anim.SetBool("run", horizontalInput != 0);
    anim.SetBool("grounded", isGrounded());

    //Jump
    if (Input.GetKeyDown(KeyCode.Space))
        Jump();

    //Adjustable jump height
    if (Input.GetKeyUp(KeyCode.Space) && body.velocity.y > 0)
        body.velocity = new Vector2(body.velocity.x, body.velocity.y / 2);

    if (onWall())
    {
        body.gravityScale = 0;
        body.velocity = Vector2.zero;
    }
    else
    {
        body.gravityScale = 7;
        body.velocity = new Vector2(horizontalInput * speed, body.velocity.y);

        if (isGrounded())
        {
            coyoteCounter = coyoteTime; //Reset coyote counter when on the ground
            jumpCounter = extraJumps; //Reset jump counter to extra jump value
        }
        else
            coyoteCounter -= Time.deltaTime; //Start decreasing coyote counter when not on the ground
    }
}

private void Jump()
{
    if (coyoteCounter <= 0 && !onWall() && jumpCounter <= 0) return; 
    //If coyote counter is 0 or less and not on the wall and don't have any extra jumps don't do anything

    SoundManager.instance.PlaySound(jumpSound);

    if (onWall())
        WallJump();
    else
    {
        if (isGrounded())
            body.velocity = new Vector2(body.velocity.x, jumpPower);
        else
        {
            //If not on the ground and coyote counter bigger than 0 do a normal jump
            if (coyoteCounter > 0)
                body.velocity = new Vector2(body.velocity.x, jumpPower);
            else
            {
                if (jumpCounter > 0) //If we have extra jumps then jump and decrease the jump counter
                {
                    body.velocity = new Vector2(body.velocity.x, jumpPower);
                    jumpCounter--;
                }
            }
        }

        //Reset coyote counter to 0 to avoid double jumps
        coyoteCounter = 0;
    }
}

private void WallJump()
{
    body.AddForce(new Vector2(-Mathf.Sign(transform.localScale.x) * wallJumpX, wallJumpY));
    wallJumpCooldown = 0;
}

private bool isGrounded()
{
    RaycastHit2D raycastHit = Physics2D.BoxCast(boxCollider.bounds.center, boxCollider.bounds.size, 0, Vector2.down, 0.1f, groundLayer);
    return raycastHit.collider != null;
}
private bool onWall()
{
    RaycastHit2D raycastHit = Physics2D.BoxCast(boxCollider.bounds.center, boxCollider.bounds.size, 0, new Vector2(transform.localScale.x, 0), 0.1f, wallLayer);
    return raycastHit.collider != null;
}
public bool canAttack()
{
    return horizontalInput == 0 && isGrounded() && !onWall();
}

}