add custom metabox per page

metabox-page.php

<?php

function theme_metabox_per_page() {
    global $pagenow;

    if ( $pagenow == 'post.php' ) {
        $page_id = ( $_SERVER['REQUEST_METHOD'] == 'POST' && $_POST['post_ID'] ) ? $_POST['post_ID'] : $_GET['post'];

        if ( $page_id ) {
            $page_slug = get_post_field( 'post_name', $page_id );

            if ( $page_slug == 'about-us' ) {
                about_page_metabox();
            }

            if ( $page_slug == 'contact' ) {
                contact_page_metabox();
            }
        }
    }
}
add_action( 'init', 'theme_metabox_per_page', 1 );

function about_page_metabox() {
    // setup about metabox here
}

function contact_page_metabox() {
    // setup contact metabox here
}