YouTube - Redirect /shorts/ and /live/

youtube-redirect-shorts.user.js

// ==UserScript==
// @name         YouTube - Redirect /shorts/ and /live/
// @namespace    https://gist.github.com/lbmaian/c53f48e04a3303d059c042f779a82604
// @downloadURL  https://gist.github.com/lbmaian/c53f48e04a3303d059c042f779a82604/raw/youtube-redirect-shorts.user.js
// @updateURL    https://gist.github.com/lbmaian/c53f48e04a3303d059c042f779a82604/raw/youtube-redirect-shorts.user.js
// @version      0.4
// @description  Redirects YouTube "/shorts/" and "/live/" URLs to "/watch?v=" URLs
// @author       lbmaian
// @match        https://*.youtube.com/*
// @grant        window.onurlchange
// @icon         https://www.youtube.com/favicon.ico
// ==/UserScript==

(function() {
    'use strict';
    function onurlchange() {
        let pathSegments = location.pathname.split('/', 3);
        if (pathSegments[1] === 'shorts' || pathSegments[1] === 'live') {
            let newSearch = location.search;
            if (newSearch[0] === '?') {
                newSearch = '&' + newSearch.substring(1);
            }
            let newHref = location.origin + '/watch?v=' + pathSegments[2] + newSearch + location.hash;
            console.log("Redirecting %s to %s", location.href, newHref);
            location.replace(newHref);
        }
    }
    if (window.onurlchange === null) { // if onurlchange supported
        window.addEventListener('urlchange', onurlchange);
    } else {
        window.setInterval(onurlchange, 500);
    }
    onurlchange();
})();

If using the Enhancer for YouTube extension, this is userscript is no longer useful with that extension's new "Convert Shorts" option

0.2: Updated to work on m.youtube.com as well
0.2.2: Add update URL and rename to "Redirect shorts" - this may require a uninstall+reinstall

0.3: Also redirect /live/ in addition to /shorts/ (and rename script accordingly)
edit: but keep update url the same: https://gist.github.com/lbmaian/c53f48e04a3303d059c042f779a82604/raw/youtube-redirect-shorts.user.js

0.4: fix bug where query params in the original URL (like ?t=123) were effectively clobbered

Perfect