Adding Archive Pages to WordPress Menus https://matthewspencer.me/notes/archive-pages-in-menus

1_create_taxonomy.php

<?php

/**
 * Register Archive Pages Taxonomy
 */
add_action( 'init', function () {

    register_taxonomy( 'archive_pages', 'nav_menu_item', array(
        'labels' => array(
            'name' => 'Archive Pages',
            'singular_name' => 'Archive Page',
        ),
        'show_ui' => false,
        'show_in_nav_menus' => true,
        'query_var' => false,
        'rewrite' => false,
    ) );

} );

2_create_terms.php

<?php

/**
 * Create Archive Pages Terms
 */
add_action( 'init', function () {

    static $terms_created = false;

    if ( ! $terms_created ) {

        $post_types = get_post_types( array(
            'publicly_queryable' => true,
            '_builtin' => false,
        ), 'objects' );
        $taxonomy = 'archive_pages';

        foreach ( $post_types as $term_name => $term ) {

            if ( term_exists( $term_name, $taxonomy ) ) {
                continue;
            }

            wp_insert_term( $term->label, $taxonomy, array( 'slug' => $term_name ) );

        }

        $terms_created = true;

    }

} );

3_filter_term_link.php

<?php

/**
 * Filter Term Link
 * Replace term link with corresponding archive page link
 *
 * @param string $link
 * @param object $term
 * @param string $taxonomy
 *
 * @return string $link
 */
add_filter( 'term_link', function ( $link, $term, $taxonomy ) {

    if ( 'archive_pages' !== $taxonomy ) {
        return $link;
    }

    $terms = namespace_get_archive_page_terms();

    $found_term = array_filter( $terms, function ( $current_term ) use ( $term ) {

        if ( $term->slug !== $current_term['name'] ) {
            return false;
        }

        return true;

    } );

    if ( ! empty( $found_term ) && ! empty( $found_term[ $term->slug ]['link'] ) ) {
        $link = $found_term[ $term->slug ]['link'];
    }

    return $link;

}, 10, 3 );

/**
 * Get Archive Page Terms
 *
 * @return array $terms
 */
function namespace_get_archive_page_terms() {

    if ( $terms = wp_cache_get( 'namespace_archive_page_terms' ) ) {
        return maybe_unserialize( $terms );
    }

    $post_types = get_post_types( array( 'public' => true ), 'names' );

    $terms = array_map( function ( $post_type ) {

        return array(
            'name' => $post_type,
            'link' => get_post_type_archive_link( $post_type ),
        );

    }, $post_types );

    wp_cache_set( 'namespace_archive_page_terms', maybe_serialize( $terms ), false, DAY_IN_SECONDS );

    return $terms;

}

4_add_current_class.php

<?php

/**
 * Add the current menu item class for post type archives.
 *
 * @param  array  $classes
 * @param  object $item
 * @return array  $classes
 */
add_filter( 'nav_menu_css_class', function ( $classes, $item ) {

    $taxonomy = 'archive_pages';

    if ( $taxonomy !== $item->object ) {
        return $classes;
    }

    $term = get_term( $item->object_id, $taxonomy );
    $post_type = $term->slug;

    if ( is_singular( $post_type ) ) {
        $classes[] = 'current-menu-parent';
    }
    else if ( is_post_type_archive( $post_type ) ) {
        $classes[] = 'current-menu-item';
    }

    return $classes;

}, 10, 2 );