How to display Posts from a Category in columns using Display Posts Shortcode. https://sridharkatakam.com/how-to-display-posts-from-a-category-in-columns-using-display-posts-shortcode/

functions.php

// Register a custom image size for Featured Category images
add_image_size( 'featured-cat-image', 300, 200, true );

/**
 * Add Column Classes to Display Posts Shortcodes
 * @author Bill Erickson
 * @link http://www.billerickson.net/code/add-column-classes-to-display-posts-shortcode
 *
 * Usage: [display-posts columns="2"]
 *
 * @param array $classes
 * @param object $post
 * @param object $query
 * @return array $classes
 */
function be_display_post_class( $classes, $post, $listing, $atts ) {
	if( !isset( $atts['columns'] ) )
		return $classes;

	$columns = array( '', '', 'one-half', 'one-third', 'one-fourth', 'one-fifth', 'one-sixth' );
	$classes[] = $columns[$atts['columns']];
	if( 0 == $listing->current_post || 0 == $listing->current_post % $atts['columns'] )
		$classes[] = 'first';
	return $classes;
}
add_filter( 'display_posts_shortcode_post_class', 'be_display_post_class', 10, 4 );

gistfile1.txt

[display-posts category="featured" posts_per_page="12" wrapper="div" wrapper_class="featured-posts-grid" image_size="featured-cat-image" columns="3"]

style.css

.featured-posts-grid .listing-item {
	margin-bottom: 40px;
}

.listing-item img {
	vertical-align: top;
}

.featured-posts-grid .listing-item a.image {
	display: block;
}