Custom query for sidebar isn't returning results

Based on our chat in the comments here’s what I came with. Please advise if it works.

<?php
function primary_category_query_shortcode( $post, $atts ) {
    //global $post;  //Uncomment this global if it still doesn't work.
    $atts = shortcode_atts( $defaults, $atts, 'primary_category_query' );
    $my_meta = get_post_meta ( $post->ID, '_yoast_wpseo_primary_category', true );
    // WP_Query arguments
    $args = array (
        'posts_per_page'         => '4',
        'meta_query'             => array(
            array(
                'key'       => '_yoast_wpseo_primary_category',
                'value'     => $my_meta
            ),
        ),
    );
    // All this would do is echo the ID of the category, correct?  Just for testing?
    //echo get_post_meta( get_the_ID(), '_yoast_wpseo_primary_category', true);  
    // The Query
    $query = new WP_Query( $args );
    // The Loop
    if ( $query->have_posts() ) { ?>
        <section class="recent-posts clear">
        <?php while ( $query->have_posts() ) : $query->the_post() ; ?>
            <article id="post-<?php the_ID(); ?>" <?php post_class( 'left' ); ?>>
                <a href="https://wordpress.stackexchange.com/questions/364402/<?php the_permalink(); ?>" title="<?php the_title_attribute(); ?>">
                    <?php the_title(); ?>
                </a>
            </article>
        <?php endwhile; ?>
        </section>
    <?php } else {
        echo 'Sorry, no more found.';
    }
    /* Restore original Post Data */
    wp_reset_postdata();
}
?>

An explanation, what I suspect may be happening is that your attempt to get the Yoast Primary Category isn’t succeeding because, based on your var_dump() you’re not getting the post ID, it’s coming back as NULL. So instead we’ll include the $post in the function() and if that still doesn’t work, we’ll use global $post; to make sure it’s being referenced. (That would be the second line, just uncomment it if it doesn’t work without it.)

I’ve also commented out the echo get_post_meta( get_the_ID(), '_yoast_wpseo_primary_category', true ); because that would, in theory, just echo out the ID number of the category. So I assumed you had that in there for testing.

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