userscripts/yt-activity.user.js

// ==UserScript==
// @name         Youtube Activity Updater
// @namespace    Youtube Activity Updater
// @version      1
// @description  Automatically updates "user activity" in youtube. Prevents 'Video paused' dialogue.
// @match        https://www.youtube.com/*
// @grant        none
// ==/UserScript==

(() => {
  'use strict';
  if(window._lact_updater) clearTimeout(window._lact_updater); 
  window._lact_updater = setInterval(() => {
    window._lact = Date.now();
  }, 300000);
})();