Adding one line of code in my project changes the whole program dramatically, please assist me?

So I only have a week’s worth of HTML, CSS, and JavaScript experience, and I’ve been trying to create a game similar to the Dinosaur game on Chrome. I’ve come across a problem trying to store a High Score. For some reason, when I try to update the normal score, the whole game disappears.
Here’s my insulting code:

HTML

<!DOCTYPE html>
<html lang="en" onclick="jump()">
  <head>
    <style>
        #title
        {
            left: 2px;
            position: relative;
        }
        #highscore 
        {
            left: 450px;
            top: 23px;
            position: fixed;
        }
    </style>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Block Game</title>
    <link rel="stylesheet" href="style.css" />
  </head>
  <body>
    <h3 id="title">Block Game</h3>
    <div id="game">
      <div id="score">Score: <br>0</br><div>
      <div id="highscore">Highscore: <br>0</br></div>
      <div id="character"></div>
      <div id="longBlock"></div>
      <div id="block"></div>
    </div>
    <script src="script.js"></script>
  </body>
</html>

CSS

* {
    padding: 0;
    margin: 0;
  }
  #game {
    width: 520px;
    height: 200px;
    left: 2px;
    position: relative;
    border: 1px solid black;
  }
  #character {
    width: 20px;
    height: 50px;
    left: 20px;
    background-color: grey;
    position: relative;
    top: 114px;
  }
  .animate {
    animation: jump 500ms;
  }
  #block {
    width: 20px;
    height: 20px;
    background-color: red;
    position: relative;
    top: 74px;
    left: 500px;
    animation: block 1.5s infinite linear;
  }
  #longBlock {
    width: 40px;
    height: 20px;
    background-color: blue;
    position: relative;
    top: 94px;
    left: 500px;
    animation: block 2s infinite linear;
  }
  @keyframes block {
    0% {
      left: 480px;
    }
    100% {
      left: -40px;
    }
  }
  @keyframes jump {
    0% {
      top: 114px;
    }
    20% {
      top: 67px;
    }
    30% {
      top: 62px;
    }
    70% {
      top: 62px;
    }
    90% {
      top: 109px;
    }
    100% {
      top: 114px;
    }
  }

JavaScript

var score = 0;
var highscore = 0;
var character = document.getElementById("character");
var block = document.getElementById("block");
var longBlock = document.getElementById("longBlock");
document.getElementById("highscore").innerHTML = "High Score: n" + highscore; 
document.getElementById("score").innerHTML = "Score: n" + score;
localStorage.clear();
window.onload = function()
{
    var scoreFromBrowser = localStorage.getItem("highscore");
    if(scoreFromBrowser!= undefined)
    {
    highscore = scoreFromBrowser;
    document.getElementById("highscore").innerHTML = "High Score: " + highscore; 
    }
}

var addScore  = setInterval(function(){
    score+=1;
    document.getElementById("score").innerHTML = "Score: n" + score;
    if(score>highscore) 
    {
        localStorage.setItem("highscore", highscore);
        highscore = score;
        document.getElementById("highscore").innerHTML = "High Score: n" + highscore; 
    }
},200);

function jump(){
    if(character.classList!="animate"){
        character.classList.add("animate");
    }
    setTimeout(function(){
        character.classList.remove("animate");
    },500);
}

var checkDead  = setInterval(function(){
    var characterTop = 
    parseInt(window.getComputedStyle(character).getPropertyValue("top"));
    var blockLeft = 
    parseInt(window.getComputedStyle(block).getPropertyValue("left"));
    var longBlockLeft = 
    parseInt(window.getComputedStyle(longBlock).getPropertyValue("left"));
    if(blockLeft<44 && blockLeft>=5 && characterTop<=130 && characterTop>=84)
    {   
        block.style.animation = "none";
        alert("You Lose. Highscore: " + highscore);
        if(!alert('Replay?'))
        {
            window.location.reload();
        } 
    }
    else if(longBlockLeft<43 && longBlockLeft>=5 && characterTop<=130 && characterTop>=74)
    {   
        block.style.animation = "none";
        alert("You Lose. Highscore: " + highscore);
        if(!alert('Replay?'))
        {
            window.location.reload();
        }
    }
},15);

I wrote this on VSCode and ran it with Live Server. If you delete all the parts like this, document.getElementById("score").innerHTML = "Score: n" + score; The game appears normally. Please Help.