bulkClearWatchLater.js

list = document.querySelector('#contents').querySelector('#contents').querySelector('#contents');

function openMenu() {
    list.firstChild.querySelector('#menu').querySelector('button').click()
}

function findRemoveEl() {
    const items = [...document.querySelector('tp-yt-paper-listbox#items').querySelectorAll('yt-formatted-string')];
    return items.find(i => i.textContent.includes('Remove from Watch Later'));
}

sleep = ms => new Promise(resolve => setTimeout(resolve, ms));
openRemoveDelay = 100;

async function iter() {
  openMenu();
  await sleep(openRemoveDelay);
  findRemoveEl().click();
}

countEl = 'todo'; // assign this to the 'x,xxx' videos element

async function smartIter() {
  const startText = countEl.textContent;
  await iter();
  
  while (true) {
    if (countEl.textContent !== startText) {
      break;
    }
    await sleep(50);
  }

  console.log(countEl.textContent);
}

async function smartIterLoop() {
  while (countEl.textContent.trim() !== '3') {
    const start = Date.now();
    await smartIter();
    console.log(Date.now() - start);
  }
}