Greasy Fork

Seems you need add a new source for "waitForKeyElements.js "(which can't be loaded "error 500"):
Maybe this one ?:
waitForKeyElements.js

or add the its original code inside at the begining (work):
/**

* @param obj - {
* sel: 'a', // the selector you want to wait for (optional)
* context: document.body, // scope of search for selector or mutations (optional, default document.body)
* stop: true, // stop waiting after first result (optional, default false)
* mode: 'M', // M to use mutation observer, S to use setInterval (optional, default M)
* onchange: func, // if using mode 'M' this function will be called whenever mutation handler triggers
* onmatch: func, // if selector is specified function will be called for each match with element as parameter
* config: { attributes: true } // if using mode 'M' this object will override settings passed to mutation observer
* }
*/
function waitForElems(obj) {
var tick;
var id = 'fke' + Math.floor(Math.random() * 12345);
var type = window.MutationObserver ? (obj.mode || 'M') : 'S';
var lastMutation = Date.now();
var lastCall = Date.now();
var context = obj.context;
var sel = obj.sel;
var config = obj.config || {
subtree: true,
childList: true
};
var onChange = obj.onchange;
var queuedCall;
var domLoaded = document && document.readyState !== 'loading';

function throttle(func) {
var now = Date.now();
clearTimeout(queuedCall);
// less than 100ms since last mutation
if (now - lastMutation < 100) {
// 500ms or more since last query
if (now - lastCall >= 500) {
func();
} else {
queuedCall = setTimeout(func, 100);
}
} else {
func();
}
lastMutation = now;
}

function findElem(sel) {
lastCall = Date.now();
var found = [].filter.call(context.querySelectorAll(sel), function(elem) {
return elem.dataset[id] !== 'y';
});
if (found.length > 0) {
if (obj.stop) {
type === 'M' ? tick.disconnect() : clearInterval(tick);
}
found.forEach(function(elem) {
elem.dataset[id] = 'y';
obj.onmatch(elem);
});
}
}

function connect() {
context = context || document.body;
if (type === 'M') {
tick = new MutationObserver(function() {
if (sel) throttle.call(null, findElem.bind(null, sel));
if (onChange) onChange.apply(this, arguments);
});
tick.observe(context, config);
} else {
tick = setInterval(findElem.bind(null, sel), 300);
}
if (sel) findElem(sel);
}

if(domLoaded) {
connect();
} else {
window.addEventListener('DOMContentLoaded', connect);
}

return {
type: type,
stop: function() {
if (type === 'M') {
tick.disconnect();
} else {
clearInterval(tick);
}
},
resume: connect
};
}
/**
* @param regex - should match the site you're waiting for
* @param action - the callback that will be executed when a matching url is visited
* @param stopLooking - if true the function will stop waiting for another url match after the first match
*/
function waitForUrl(regex, action, stopLooking) {
function checkUrl(urlTest) {
var url = window.location.href;
if (url !== lastUrl && urlTest(url)) {
if (stopLooking) {
clearInterval(tick);
}
lastUrl = url;
action();
}
lastUrl = url;
}
var urlTest = (typeof regex === 'function' ? regex : regex.test.bind(regex)),
tick = setInterval(checkUrl.bind(null, urlTest), 300),
lastUrl;
checkUrl(urlTest);
return tick;
}
// ADD OTHER CODE AFTER


Re edit:

This require seems working (from Auto Close YouTube Ads):
// @require https://cdn.jsdelivr.net/gh/fuzetsu/userscripts@ec863aa92cea78a20431f92e80ac0e93262136df/wait-for-elements/wait-for-elements.js