display terms that match query heirarchy

heirarchical-terms.php

<?php
// terms that match the tax archives heierarchy
// show only parent terms in parent archives
// show only child terms in child archives

function custom_get_terms() {
    // set the taxonomy
    $tax_name = 'category';
    // is archive parent or child logic
    $current_term = get_queried_object();
    $is_parent = $current_term->parent == 0 ? true : false;
    // get the terms
    $terms = get_the_terms( get_the_ID(), $tax_name );
    $html = '<ul class="custom-terms">';

    foreach( $terms as $key => $term ) {
        if ( ( $is_parent && $term->parent == 0 ) || ( !$is_parent && $term->parent != 0 ) ) {
            // return html if term heirarchy matches archives
            $html .= '<li><a href="' . esc_attr( get_term_link( $term->slug,  $tax_name ) ) . '">' . __( $term->name ) . '</a></li>';
        }
    }
    $html .= '</ul>';

    return $html;
}
// example use in render_block filter
add_filter( 'render_block', function( $block_content, $block ) {
    if ( 
        ! empty( $block['attrs']['className'] ) 
        && 'custom-terms' === $block['attrs']['className']  
    ) {
        $block_content = custom_get_terms();
    }

    return $block_content;
}, 10, 2 );