This userscript is designed to diagnose issues related to the modification of YouTube's video player, which might interfere with other userscripts like anti anti-adblockers

yt-observer.user.js

// ==UserScript==
// @name         YouTube: observer
// @namespace    http://tampermonkey.net/
// @version      1
// @description  try to take over the world!
// @author       You
// @match        https://www.youtube.com/*
// @icon         https://www.google.com/s2/favicons?sz=64&domain=youtube.com
// @grant        none
// @run-at       document-start
// ==/UserScript==

(function () {
  'use strict';

  const log = (message) => {

    const template = `%c[%c{{date-time}}%c] [%cObserver%c] %c{{message}}`;
    const result = template
      .replace('{{date-time}}', (new Date(Date.now() + 6e5)).toISOString())
      .replace('{{message}}', message);

    console.log(result, 'color: black', 'color: blue', 'color: black', 'color: green', 'color: black', 'color: grey');

  };

  const getNodeSymbol = (node) => {
    return `${node.tagName}.${[...node.classList].join('.')}`
  }

  const getNodeDefinitions = (node) => {
    return `<${node.tagName} ${ node.getAttributeNames().map(x => `${x}="${node.getAttribute(x)}"`).join(' ') }> </ ${node.tagName}>`
  }

  const init = () => {
    log('initializing video player observer');

    // Callback function to execute when mutations are observed
    const callback = (mutationsList, observer) => {
      for (let mutation of mutationsList) {
        if (mutation.type === 'childList') {
          for (let node of mutation.addedNodes) {

            if (node.nodeType === Node.ELEMENT_NODE && node.classList.contains('html5-main-video')) {
              log(`HTML5 video ${getNodeDefinitions(mutation.target)} added`);
            }

          }
        }
        else if (mutation.type === 'attributes') {
          if (mutation.target.classList.contains('html5-video-container')) {
            log(`Attribute '${mutation.attributeName}' of ${getNodeSymbol(mutation.target)} was modified.`);
            log(`after modifications it looks like ${getNodeDefinitions(mutation.target)}`);
          }
          else {
            if (mutation.target.tagName === 'VIDEO') {
              log(`Attribute '${mutation.attributeName}' of ${getNodeSymbol(mutation.target)} was modified.`);
              log(`after modifications it looks like ${getNodeDefinitions(mutation.target)}`);
            }
          }
        }
      }
    };

    // Create an observer instance linked to the callback function
    const observer = new MutationObserver(callback);
    const config = {
      childList: true,
      subtree: true,
      attributes: true
    };

    const startObserving = () => {
      if (document.body) {
        observer.observe(document.body, config);
        log('observer has been attached and it`s working');
      } 
      else {
        requestAnimationFrame(startObserving);
      }
    };

    // Start trying to observe
    startObserving();
  };

  init();

})();