Try it like this:
$categories = get_the_category();
echo '<ul>';
echo '<li> Parent Category: ';
foreach( $categories as $category ){
if($category->parent != 0){
$parent_category = get_term( $category->parent );
echo '<a href="' . esc_url( get_category_link($parent_category->term_id)) . '">' . esc_html($parent_category->name) . ' </a>';
break;
}
}
echo '</li>';
echo '<li>Subcategory: ';
foreach( $categories as $category ){
if($category->parent != 0){
echo '<a href="' . esc_url( get_category_link($category->term_id)) . '">' . esc_html($category->name) . ' </a>';
}
}
echo '</li></ul>';
This works pretty well if your post’s categories have the same parent category (e.g Your post has the categories ‘child_1’ and ‘child_2’ which are both children of the category ‘parent_1’). It checks each of your post’s categories. In the first foreach-loop, as soon as a category has a parent category it will be echoed and the loop will be left because of the break.
But if your post has multiple categories with different parent categories (e.g Your post has the category ‘child_A_1’ which is a child of ‘parent_A’, and the category ‘child_B_1’ which is a child of ‘parent_B’) this code won’t work correctly since it would only echo the parent-category of the first subcategory that occurs in the first foreach-loop.