Open a popup that dynamically loads a video based on the click open trigger using 1) data attribute or 2) a query parameter

send_video_link_to_popup_data_attribute.php

<?php // Ignore this first line when copying to your child theme's functions.php file.

/**
 * Send a video link to a popup using a URL in a data attribute.
 */
function send_video_link_to_popup()
{ ?>
	<script type="text/javascript">
		jQuery(document).ready(function($) {
			const popupID = 85, // Change to your popup IDs.
				defVid = 'i9chqRlu1E4'; // We need to use the original video ID in the popup as a placeholder.

			let vid = '';

			// Before the vid popup opens, check for the query param and then process
			// the new vid link to inject into the popup's iframe.
			$(document).on('pumBeforeOpen', `#pum-${popupID}`, function() {
				const trigger = $.fn.popmake.last_open_trigger[0].firstChild, // Grab the popup trigger's link element.
					link = trigger.dataset.video; // Grab the video attribute from the trigger.

				// If the link has something, continue.
				if (link && "" !== link) {
					const url = new URL(link); //, // Grab the URL from the link.

					const ytIframe = $(`#pum-${popupID} iframe`);
					const src = ytIframe.prop('src');

					const tmpArr = link.split('/');
					vid = tmpArr[tmpArr.length - 1]; // The the last entry in the array should be the new vid ID.
					//console.log(`[DEBUG] link: ${link} src: ${src} vid: ${vid}`);
					ytIframe.prop('src', src.replace(defVid, vid)); // Swap vid IDs.

				} // if

			}); // listener

			// Reset things since we're reusing the same popup for diffent videos.
			$(document).on('pumBeforeClose', `#pum-${popupID}`, function() {
				const ytIframe = $(`#pum-${popupID} iframe`),
					src = ytIframe.prop('src');
				ytIframe.prop('src', src.replace(vid, defVid)); // Reset to the placeholder vid ID.
			}); // listener

		}); // jQuery
	</script>
<?php }
add_action('wp_footer', 'send_video_link_to_popup', 500); // Load the script in the footer with a "late" priority.

/**
 * You can add the PHP code snippet to your child theme's functions.php file
 * or with third-party plugins such as My Custom Functions and Code Snippets.
 *
 * Learn more:
 * - https://wppopupmaker.com/docs/getting-started-with-custom-code/getting-started-with-custom-js/
 * - https://wppopupmaker.com/docs/getting-started-with-custom-code/getting-started-with-custom-php/
 */

send_video_link_to_popup_query_parameter.php

<?php // Ignore this first line when copying to your child theme's functions.php file.

/**
 * Send a video link to a popup using a query parameter.
 *
 * Based on https://youtu.be/zml-xz78o2Q
 */
function send_video_link_to_popup() { ?>
 	<script type="text/javascript">
		jQuery(document).ready(function ($) {
			const popupID = 2114, // Change to your popup IDs.
				defVid = '2E1Pw39TtFM'; // We need to use the original video ID in the popup as a placeholder.
			
			let hasQueryParameter = false,
				vid = '';

			// Before the vid popup opens, check for the query param and then process
			// the new vid link to inject into the popup's iframe.
    			$(document).on('pumBeforeOpen', `#pum-${popupID}`, function () {
        			const trigger = $.fn.popmake.last_open_trigger[0].firstChild, // Grab the popup trigger's link element.
					link = trigger.href; // Grab the href attribute from the trigger.
				
				// If the link has something, continue.
      				if (link && "" !== link) {
					const url = new URL(link), // Grab the URL from the link.
						searchParams = new URLSearchParams(url.search); // Grab the query parameters.
        				if (!searchParams.get('usepopup')) return; // Bail if no popup query parameter.
					hasQueryParameter = true;
					
					const ytIframe = $(`#pum-${popupID} iframe`);
           				const src = ytIframe.prop('src');
					
					const tmpArr = link.split('/');
					vid = tmpArr[tmpArr.length - 2]; // The second to the last entry in the array should be the new vid ID.
					console.log(`[DEBUG] link: ${link} src: ${src} vid: ${vid}`);
					ytIframe.prop('src', src.replace(defVid, vid)); // Swap vid IDs.
				} // if
    	
      			}); // listener
			
			// Reset things since we're reusing the same popup for diffent videos.
    			$(document).on('pumBeforeClose', `#pum-${popupID}`, function () {
				if (!hasQueryParameter) return; // Bail if no popup query parameter.
				const ytIframe = $(`#pum-${popupID} iframe`);
				const src = ytIframe.prop('src');
        			ytIframe.prop('src', src.replace(vid, defVid)); // Reset to the placeholder vid ID.
      			}); // listener
			
    		}); // jQuery
 	</script>
<?php }
add_action( 'wp_footer', 'send_video_link_to_popup', 500 ); // Load the script in the footer with a "late" priority.

/**
 * You can add the PHP code snippet to your child theme's functions.php file
 * or with third-party plugins such as My Custom Functions and Code Snippets.
 *
 * Learn more:
 * - https://wppopupmaker.com/docs/getting-started-with-custom-code/getting-started-with-custom-js/
 * - https://wppopupmaker.com/docs/getting-started-with-custom-code/getting-started-with-custom-php/
 */

Usage

In your post or page, add the usepopup query parameter to your video links.

https://youtu.be/mMW3pE6KSv8/?usepopup=1