<?php
// $list_subcat = get_terms( ['taxonomy' => 'category', 'hide_empty' => false, 'parent' => $cat] );
// $list_subcat = get_categories( ['hide_empty' => false, 'parent' => $cat] );

$list_subcat = array();
if ( !empty($cat) ) $list_subcat = get_categories( ['hide_empty' => false, 'parent' => $cat] );

if ( count($list_subcat)):

	echo "<div class='subcat'>";
	foreach ($list_subcat as $item_subcat) {

		$category_link = get_category_link( $item_subcat->term_id );

		echo '<div>';
		echo '<h3><a href="'.$category_link.'">'.$item_subcat->name.'</a></h3>';
		echo '<div><a href="'.$category_link.'">'.$item_subcat->description.'</a></div>';
		echo '</div>';
	}
	echo "</div>";

endif