Enable .current-menu-ancestor for WP core navigation item block

navigation-item.php

<?php
/**
 * Plugin Name: Navigation Item Ancestors
 */

namespace Config\Navigation_Item;

function get_post_children_ids(): array {
	static $children_ids;

	if ( ! isset( $children_ids ) ) {
		$children_ids = [];

		// Get all posts with a parent set.
		$query = new \WP_Query(
			[
				'post_type' => 'any',
				'post_status' => 'publish',
				'posts_per_page' => -1,
				'fields' => 'id=>parent',
				'post_parent__not_in' => [ 0 ], // Exclude posts without parents.
				'no_found_rows' => true,
				'cache_results' => true,
				'update_post_term_cache' => false,
				'update_post_meta_cache' => false,
			]
		);

		if ( ! empty( $query->posts ) ) {
			$children_ids = array_reduce(
				$query->posts,
				function ( $carry, $post ) {
					$carry[ $post->post_parent ][] = $post->ID;

					return $carry;
				},
				[]
			);

			// Now collect all ancestry.
			foreach ( $children_ids as $parent_id => $child_ids ) {
				foreach ( $child_ids as $child_id ) {
					if ( isset( $children_ids[ $child_id ] ) ) {
						$children_ids[ $parent_id ] = array_merge( $children_ids[ $parent_id ], $children_ids[ $child_id ] );
					}
				}
			}
		}
	}

	return $children_ids;
}

add_filter(
	'render_block',
	function ( $block_content, $block ) {
		if ( ! empty( $block['attrs']['id'] ) && str_starts_with( $block['blockName'], 'core/navigation-' ) && is_singular() ) {
			$children_ids = get_post_children_ids();
			$current_post_id = get_queried_object_id();
			$menu_link_post_id = (int) $block['attrs']['id'];

			if ( isset( $children_ids[ $menu_link_post_id ] ) && in_array( $current_post_id, $children_ids[ $menu_link_post_id ], true ) ) {
				return str_replace(
					' wp-block-navigation-item',
					' wp-block-navigation-item current-menu-ancestor',
					$block_content
				);
			}
		}

		return $block_content;
	},
	10,
	2
);