functions.php

<?php 

/**
 * Display only sticky posts
 * @see https://displayposts.com/2019/01/09/display-or-hide-sticky-posts/
 *
 */
function be_display_only_sticky_posts( $args, $atts ) {

	$sticky_variations = array( 'sticky_posts', 'sticky-posts', 'sticky posts' );
	if( !empty( $atts['id'] ) && in_array( $atts['id'], $sticky_variations ) ) {
		$sticky_posts = get_option( 'sticky_posts' );
		$args['post__in'] = $sticky_posts;
	}

	if( !empty( $atts['exclude'] ) && in_array( $atts['exclude'], $sticky_variations ) ) {
		$sticky_posts = get_option( 'sticky_posts' );
		$args['post__not_in'] = $sticky_posts;
	}
	
	return $args;
}
add_filter( 'display_posts_shortcode_args', 'be_display_only_sticky_posts', 10, 2 );