open-youtube-app.user.js

// ==UserScript==
// @name         Open YouTube App
// @version      1.0.4
// @author       ryuya
// @match        *://*.youtube.com/*
// @downloadURL  https://gist.github.com/ryuya0124/2ba4f56cf9e9dab781d3146c74a3f36b/raw/36b9e3e13a95a4e323ff99b22b104bc61abaf764/open-youtube-app.user.js
// @updateURL    https://gist.github.com/ryuya0124/2ba4f56cf9e9dab781d3146c74a3f36b/raw/36b9e3e13a95a4e323ff99b22b104bc61abaf764/open-youtube-app.user.js
// @homepage     https://gist.github.com/ryuya0124/2ba4f56cf9e9dab781d3146c74a3f36b
// ==/UserScript==

if (window.location.pathname === '/redirect') return;

let targetUrl = '';

if (window.location.pathname.startsWith('/@')) {
  // Handle URLs with @username
  const username = window.location.pathname.slice(2);
  targetUrl = `youtube://www.youtube.com/@${username}${window.location.search}${window.location.hash}`;
} else {
  // Handle regular video/channel URLs
  targetUrl = `youtube://${window.location.pathname.slice(1)}${window.location.search}${window.location.hash}`;
}

window.location.href = targetUrl;