Custom Post Type Related Posts to Your WordPress Site Without Plugins. All the codes need to add in your single.php add this code snippet after the post loop end.

single.php

$related = new WP_Query(
    array(
        'post_type'      => 'tutorials', //YOUR CPT SLUG
        'category__in'   => wp_get_post_categories( $post->ID ),
        'posts_per_page' => 3,
        'post__not_in'   => array( $post->ID ),
    )
);

if ( $related->have_posts() ) { ?>
<h3><?php _e( 'You might like this too!', 'hoolite' ); ?></h3>
<div class="cpt-list">
    <?php
    while ( $related->have_posts() ) {
        $related->the_post();
        ?>
        <div class="cpt-post">
            <div class="cpt-post--wrapper">
                <?php
                $featured_image = get_the_post_thumbnail_url(get_the_ID(),'medium'); // THUMBNAIL, MEDIUM, LARGE, FULL.
                $default_image = get_site_url() .'/wp-content/uploads/2022/02/my_backup_image.jpg'; // URL TO YOUR DEFAULT/BACKUP IMAGE.
                $post_thumbnail = has_post_thumbnail( $post->ID ) ? $featured_image : $default_image; // CHECK IF FEATURED IMAGE ELSE USE DEFAULT IMAGE ?>

                <a href="<?php echo esc_url( get_the_permalink() ); ?>" title="<?php echo esc_html( the_title() ); ?>">
                    <div class="cpt-post--thumb" style="background-image: url('<?php echo $post_thumbnail ?>')"></div>
                </a>
                <div class="cpt-post--text-inner">
                    <a href="<?php echo esc_url( get_the_permalink() ); ?>" title="<?php echo esc_html( the_title() ); ?>"><h3><?php echo esc_html( get_the_title() ); ?></h3></a>
                    <?php echo wp_trim_words( get_the_content(), 25 ); ?>
                </div>
            </div>
        </div>
        <?php
    }
    wp_reset_postdata();
    ?>
</div>
<?php
} else {
    esc_html_e( 'Woops! Nothing found!', 'hoolite' );
}

style.css

.cpt-list {
    display: flex;
    flex-wrap: wrap;
    margin: 0 -16px;
}
.cpt-list .cpt-post {
    padding: 0 16px;
    margin-bottom: 32px;
    width: 33.33%;
}
.cpt-list .cpt-post .cpt-post--text-inner {
    padding: 16px;
}
.cpt-list .cpt-post .cpt-post--thumb {
    height: 200px;
    background-size: cover;
    background-position: center;
}
.cpt-list .cpt-post .cpt-post--wrapper{
    box-shadow: 4px 8px 40px 0 rgb(0 0 0 / 10%);
    height: 100%;
}