<?php

add_shortcode( 'articles_posts', 'articles_posts_shortcode' );

function articles_posts_shortcode($atts) {
    $the_query = new WP_Query( [
        'tax_query'           => [
            [
                'taxonomy' => 'category',
                'field'    => 'slug',
                'terms'    => $atts['slug'],
            ],
        ],
        'nopaging'      => true,
    ] );


    foreach ($the_query->posts as $post) {
        ?>
        <p><?=$post->post_title?></p>
        <p><?=get_the_excerpt($post);?></p>
        <p><?=get_the_post_thumbnail( $post->ID );?></p>
        <?php
    }
}
?>