Notes

using UnityEngine;
using UnityEngine.UI;

public class BlockBreaker : MonoBehaviour
{
public int score = 0;
public Text scoreText;

public Rigidbody2D ballPrefab;
public Transform ballSpawnPoint;
public float ballInitialSpeed = 5f;

public float paddleSpeed = 5f;
public Transform paddle;

public GameObject[] blocks;
public int numBlocks = 20;
public float blockSpacing = 0.5f;
public float blockMoveSpeed = 1f;

private Rigidbody2D ball;
private bool ballInPlay = false;
private bool gameOver = false;

void Start()
{
SpawnBall();
SpawnBlocks();
}

void Update()
{
if (Input.GetKeyDown(KeyCode.Space) && !ballInPlay)
{
ball.velocity = new Vector2(ballInitialSpeed, ballInitialSpeed);
ballInPlay = true;
}

float horizontalInput = Input.GetAxis("Horizontal");
paddle.Translate(new Vector3(horizontalInput * paddleSpeed * Time.deltaTime, 0f, 0f));

// clamp paddle position to screen bounds
Vector3 paddlePosition = paddle.position;
paddlePosition.x = Mathf.Clamp(paddlePosition.x, -8f, 8f);
paddle.position = paddlePosition;

if (gameOver)
{
if (Input.GetKeyDown(KeyCode.Space))
{
UnityEngine.SceneManagement.SceneManager.LoadScene(UnityEngine.SceneManagement.SceneManager.GetActiveScene().name);
}
}
}

void FixedUpdate()
{
if (!gameOver)
{
// move blocks down
for (int i = 0; i < numBlocks; i++)
{
blocks[i].transform.Translate(new Vector3(0f, -blockMoveSpeed * Time.deltaTime, 0f));

if (blocks[i].transform.position.y < -5f)
{
// game over
gameOver = true;
ball.velocity = Vector2.zero;
ballInPlay = false;
scoreText.text = "Game Over! Press Space to Restart.";
return;
}
}
}
}

void SpawnBall()
{
ball = Instantiate(ballPrefab, ballSpawnPoint.position, Quaternion.identity);
}

void SpawnBlocks()
{
blocks = new GameObject[numBlocks];

float startX = -3f;
float startY = 3f;

for (int i = 0; i < numBlocks; i++)
{
blocks[i] = Instantiate(Resources.Load<GameObject>("Block"), new Vector3(startX + (i % 10) * blockSpacing, startY - (i / 10) * blockSpacing, 0f), Quaternion.identity);
}
}

void OnCollisionEnter2D(Collision2D other)
{
if (other.gameObject.CompareTag("Block"))
{
Destroy(other.gameObject);
score += 10;
scoreText.text = "Score: " + score.ToString();

if (GameObject.FindGameObjectsWithTag("Block").Length == 0)
{
// level complete
gameOver = true;
ball.velocity = Vector2.zero;
ballInPlay = false;
scoreText.text = "Level Complete! Press Space to Restart.";
}
}
}
}