Delete remove all videos from Youtube "Watch Later" playlist (working as of 12/14/2020)

clear-watch-later-playlist.js

// This script can be used to clear all videos from youtube's built-in "watch later" playlist which has a limit of 5,000 videos. 
// Without this, you would need to click the remove button on each video in the list. 
// Youtube made changes recently that caused errors for a previously working script.
// Script written by: janthedeveloper (https://github.com/JanTheDeveloper)
// Bookmark wrapper added by: shelldonhull (https://github.com/sheldonhull)
// Full conversation here: https://gist.github.com/astamicu/eb351ce10451f1a51b71a1287d36880f#file-readme-md

// 1. Save the javascript text below as a bookmark in google chrome(Simply replace the URL field in any existing bookmark, and give the bookmark any name) 

	javascript:(() => {setInterval(function () {  document.querySelector('#primary button[aria-label="Action menu"]').click();  var things = document.evaluate(    '//span[contains(text(),"Remove from")]',    document,    null,    XPathResult.ORDERED_NODE_SNAPSHOT_TYPE,    null  );  for (var i = 0; i < things.snapshotLength; i++) {    things.snapshotItem(i).click();  }}, 1000); })();

// 2.) Enter this exact URL into google chrome web browswer: https://www.youtube.com/playlist?list=WL&disable_polymer=true 
     // NOTE 1: THE URL MUST END WITH "&disable_polymer=true"
     // NOTE 2: You'll need to be signed into your youtube account when using this URL, if you're not already. 

// 3.) Once you're on the correct Watch Later playlist page, click the bookmark that you saved in the step 1. This will start deleting videos. 

// Source: https://gist.github.com/astamicu/eb351ce10451f1a51b71a1287d36880f#gistcomment-3552367  (as of 12/14/2020)

// You can save any javascript snippet as a bookmark and run as needed using this format:
// 	 javascript:(() => { REPLACE_THIS_TEXT_WITH_SCRIPT })();


// If page is being displayed in language other than English, see comment from Gater73 below. Update portions on html tags that vary based on language. 

// Full script, without the bookmark wrapper code below (This could be entered into the chrome dev-tools console as an alternative to using the bookmarked script) 
	setInterval(function () { 
		document.querySelector('#primary button[aria-label="Action menu"]').click(); 
		var things = document.evaluate(    '//span[contains(text(),"Remove from")]',    document,    null,    XPathResult.ORDERED_NODE_SNAPSHOT_TYPE,    null  ); 
		 
		 for (var i = 0; i < things.snapshotLength; i++) {
			things.snapshotItem(i).click();  
		}
	}, 1000);
  

Previously posted this here

Not sure how good this is, but worked for me. Since there's no language dependent querySelector, should work for most people (I hope...)
Caveat: It might take a while, but just leave it doing it's thing

It works on this url: https://www.youtube.com/playlist?list=WL

There were over 2000+ videos on my watch later. I tried removing the ones I had already watched using the Youtube's built in feature, but the request would eventually throw me a 502 after a minute or so of waiting.

function sleep(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
}

async function deleteFirstVideo(){   
    let menu = document.querySelectorAll("yt-icon-button[class='dropdown-trigger style-scope ytd-menu-renderer']")[1]; 
    menu.click(); 

    // Tiny delay to give the menu time to render
    await sleep(300); 
    let menuItems = document.querySelector("tp-yt-paper-listbox[class='style-scope ytd-menu-popup-renderer']").children;
    
    // In case of unavailable videos, there's only the remove button
    let button = menuItems[2] ?? menuItems[0]; 
    button.click();  
}

// Just check how much you have in the playlist
let videos_count = 2000;
for (i=0; i < videos_count ; i++){ 
    deleteFirstVideo(); 
    // 1500ms would get me 429 response after a couple of requests
    await sleep(1750);
}

MacOS. Doesn't work for me because of problem below:

Uncaught TypeError: Cannot read properties of null (reading 'click')
at :1:103

How to solve this? 

@ArthurYdalgo 's code works well, without throwing into 5xx errors. Thanks