Add post thumbnail to Elementor post navigation

functions.php

<?php 

// Source: https://github.com/elementor/elementor/issues/3863#issuecomment-643794411

// Previous next post thumb
add_filter('previous_post_link', 'sydney_child_post_nav_thumbnail', 20, 5 );
add_filter('next_post_link', 'sydney_child_post_nav_thumbnail', 20, 5 );

function sydney_child_post_nav_thumbnail($output, $format, $link, $post, $adjacent) {
	if( !$output ) {
		return;
	}

	$divclass = '';
	
	switch ($adjacent) {
		case 'next':
		$divclass = 'custom-nav nav-next';
		break;
		case 'previous':
		$divclass = 'custom-nav nav-previous';
		break;
		default:
		break;
	}

	$arrow_prev = '';
	$arrow_next = '';
	
	if( 'next' == $adjacent ) {
		$arrow_next = '<span>&#10230;</span>';
	}
	if( 'previous' == $adjacent ) {
		$arrow_prev = '<span>&#10229;</span>';
	}

	$rel   = $adjacent;
	$thumb = get_the_post_thumbnail($post->ID, array( 100, 100) );
	$title = '<div class="'.$divclass.'">' . $arrow_prev . $post->post_title . $arrow_next . '</div>';

	$class = '';
	if( !empty($thumb) ) {
		$class = 'post-nav-has-thumbnail';
	}

	$string = '<a href="' . get_permalink( $post->ID ) . '" rel="' . $rel . '" class="'.$class.'">' . $thumb;
	$inlink = str_replace( '%title', $title, $link );
	$inlink = $string . $inlink . '</a>';
	$output = str_replace( '%link', $inlink, $format );

	if( !$post->ID ) {
		return;
	}

return $output;

}