Click on YouTube button inside iframe using javascript

I have a YouTube playlist displayed inside an iframe on a webpage & want to automate clicking on the playlist’s ‘index button’ when the page loads so that the list of videos is displayed.

The button has the following classes: ytp-playlist-menu-button & ytp-button but no ID. It does however have an aria-owns ytp-id-22 which after Googling, I believe acts like an ID – is that right?

As I’m not sure whether aria-owns acts like (& can be used as) an ID, I’m trying document.getElementsByClassName instead but am aware that this is not a good practice & doesn’t work on some browsers.

I’m trying to work out by looking at examples online but haven’t found a clear way to achieve this. I’m currently using the script formula below but it doesn’t work & I’m not convinced it’s the right approach either.

document.addEventListener('DOMContentLoaded', () => {
    document.querySelector('#player_2').contentWindow
        document.getElementsByClassName('ytp-playlist-menu-button').trigger("click") ;
});

You can view the actual page where the YouTube playlist is embedded here

My knowledge of writing javascript / jQuery is extremely limited but as far as I understand it, in the above code:

1. The 1st line ensures the page has fully loaded
2. The 2nd line allows it work ‘inside’ an iframe (with the ID ‘player_2’)
3. The 3rd line is the action that clicks on the button (with an ID ‘ytp-playlist-menu-button’)

Also just to say:

A. Above is the entire script & I was wondering does it need additional code to actually work properly?
B. I have enqueued the script into the header via this code:

function theme_enqueue_scripts() {
        if (is_page ('3055') ) {
            wp_enqueue_script ('youtubePlaylistButton_js', get_theme_file_uri() . '/wp-includes/js/youtubePlaylistButton_js.js', array(), false, false); }
        }
        add_action( 'wp_enqueue_scripts', 'theme_enqueue_scripts' );