Disable auto open for a popup if $_GET parameter is missing or empty.

disable-auto-open-if-GET-value-empty.php

<?php
add_action( 'popmake_get_the_popup_data_attr', 'my_custom_popup_data_attr', 10, 2 );
function my_custom_popup_data_attr( $data_attr, $popup_id ) {
	if ( $popup_id == 123 && empty( $_GET['popup'] ) ) {
		unset( $data_attr['meta']['auto_open'] );
	}
	return $data_attr;
}