am gatting error in java script to migrate manifest v2 to v3

Question

I am developing a chrome extension with manifest v2 but now google requires manifest v3. So when I try to migrate from v2 to v3, the extension is not working. But with v2 the extension was working fine.

I'm trying for the last 2 weeks but none of my ideas is working correctly. So please help and describe your ideas. Thanks, I'm a beginner in English so please don't mind that.

manifest.json v2

{
  "manifest_version": 2,
  "name": "Text Tool",
  "description": "A professional chrome extension for word and character count with and without spaces from selected text from any website.",
  "version": "1.0",
  "permissions": ["activeTab", "downloads"],
  "browser_action": {
    "default_title": "Text Tool",
    "default_popup": "popup.html"
  },
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  }
}

popup.js

function updateCounts(selectedText) {
  if (!selectedText) {
    return;
  }
  var words = selectedText.match(/\b[-?(\w+)?]+\b/gi);
  var uniqueWords = [...new Set(words)];
  var wordCount = words?.length;
  var uniqueWordCount = uniqueWords?.length;
  var charCountWithSpaces = selectedText.length;
  var charCountWithoutSpaces = selectedText.replace(/\s+/g, '').length;
  var sentenceCount = selectedText.split(/[.!?]+/g).filter(Boolean).length;
  var paragraphCount = selectedText.split(/\n+/g).filter(Boolean).length;
  var textSize = (selectedText.length / 1024).toFixed(2) + ' KB';
  var totalWordLength = words.reduce((total, word) => total + word.length, 0);
  var avgWordLength = (totalWordLength / wordCount).toFixed(2);
  var avgSentenceLengthWords = (wordCount / sentenceCount).toFixed(2);
  var avgSentenceLengthChars = (charCountWithSpaces / sentenceCount).toFixed(2);

  document.getElementById('word-count').innerHTML = wordCount;
  document.getElementById('unique-words').innerHTML = uniqueWordCount;
  document.getElementById('char-count-with-spaces').innerHTML = charCountWithSpaces;
  document.getElementById('char-count-without-spaces').innerHTML = charCountWithoutSpaces;
  document.getElementById('sentence-count').innerHTML = sentenceCount;
  document.getElementById('paragraph-count').innerHTML = paragraphCount;
  document.getElementById('text-size').innerHTML = textSize;
  document.getElementById('avg-word-length').innerHTML = avgWordLength;
  document.getElementById('avg-sentence-length-words').innerHTML = avgSentenceLengthWords;
  document.getElementById('avg-sentence-length-chars').innerHTML = avgSentenceLengthChars;

  // Calculate reading time (based on 275 words per minute)
  var readingTime = Math.ceil(wordCount / 275);
  document.getElementById('reading-time').innerHTML = readingTime + ' minute(s)';

  // Calculate speaking time (based on 150 words per minute)
  var speakingTime = Math.ceil(wordCount / 150);
  document.getElementById('speaking-time').innerHTML = speakingTime + ' minute(s)';

  // Calculate handwriting time (based on 20 words per minute)
  var handwritingTime = Math.ceil(wordCount / 20);
  document.getElementById('handwriting-time').innerHTML = handwritingTime + ' minute(s)';
}

document.addEventListener("DOMContentLoaded", function() {
  chrome.tabs.executeScript({
    code: "window.getSelection().toString();"
  }, function(selection) {
    const selectedText = selection[0];
    document.getElementById("selectedText").textContent = selectedText;
    updateCounts(selectedText);
  });

  document.getElementById("copyButton").addEventListener("click", function() {
    const textarea = document.getElementById("selectedText");
    textarea.select();
    document.execCommand("copy");
  });

  document.getElementById("exportButton").addEventListener("click", function() {
    const selectedText = document.getElementById("selectedText").textContent;
    const blob = new Blob([selectedText], { type: "text/plain;charset=utf-8" });
    const url = URL.createObjectURL(blob);
    chrome.downloads.download({
      url: url,
      filename: "selectedText.txt",
      saveAs: true
    });
  });
});