functions.php

<?php

/**
 * Display Posts, search form if no results
 * @see https://displayposts.com/2019/01/04/display-search-form-if-no-results/
 */
function be_dps_no_results_search( $message ) {

	$message = '<div class="display-posts-listing no-results">';
	$message .= '<p>It seems we can’t find what you’re looking for. Perhaps searching can help.</p>';
	$message .= get_search_form( false );
	$message .= '</div>';

	return $message;
}
add_filter( 'display_posts_shortcode_no_results', 'be_dps_no_results_search' );