Wordpress Post Loop

function blog_func($atts)
{
    $artikel = shortcode_atts(
        array(
            'anzahl_artikel' => '4',
        ), $atts);


    $args = array(
        'post_type' => 'post',
        'order_by' => 'date',
        'posts_per_page' => $artikel['anzahl_artikel'],
        'date_query' => array(
            array(
                'year',
                'month',
                'day',
            ),
        ),
    );


    $blog = '';


    $post_query = new WP_Query($args);
    if ($post_query->have_posts()) {
        while ($post_query->have_posts()) {


            $post_query->the_post();


            $blog .= '
            <div>
                <div class="uk-card uk-card-small card-muted">
                    <div class="uk-card-media-top uk-position-relative">
                        <img src="' . the_post_thumbnail(array(612, 294)) . '" />
                        <canvas></canvas>
                    </div>
                </div>
            </div>';


        }
        return $blog;
    }


}

function blog_func($atts)
{
    $artikel = shortcode_atts(
        array(
            'anzahl_artikel' => '4',
        ), $atts);


    $args = array(
        'post_type' => 'post',
        'order_by'  => 'date',
        'posts_per_page' => $artikel['anzahl_artikel'],
        'date_query' => array(
            array(
                'year',
                'month',
                'day',
            ),
        ),
    );


    $post_query = new WP_Query($args);
    if($post_query->have_posts() ) {
        while($post_query->have_posts() ) {
            $post_query->the_post();
            ?>
            <div class="uk-grid uk-child-width-1-1" uk-grid>
                <div class="uk-grid-item-match">
                    <div class="uk-card uk-grid-collapse " uk-grid>
                        <div class="uk-width-2-5@s uk-card-media-left uk-cover-container">
                            <img uk-cover src="'<?php the_post_thumbnail(array(612, 294)); ?>
                            <canvas width="600" height="400"></canvas>
                        </div>
                        <div class="uk-width-3-5@s uk-card-body">
                            <h3 class="font-thin"><?php the_title(); ?></h3>
                            <h3 class="font-thin">
                                <?php the_time('d.m.Y'); ?>
                            </h3>
                            <p><?php the_excerpt(); ?></p>
                            <div>
                                <a href=<?php the_permalink() ?>
                                   class="uk-text-primary uk-link-reset uk-button uk-button-text">mehr lesen</a>
                            </div>
                        </div>
                    </div>
                </div>
            </div>
            <?php
        }
    }


}