Add a Duplicate Post Link to the WordPress Admin Posts List

function custom_add_duplicate_post_link( $actions, $post ) {
    if (
        ! current_user_can( 'edit_posts' ) ||
        ! current_user_can( 'edit_post', $post->ID ) ||
        'trash' === $post->post_status
    ) {
        return $actions;
    }

    $url = wp_nonce_url(
        admin_url( 'admin-post.php?action=custom_duplicate_post&post=' . $post->ID ),
        'custom_duplicate_post_' . $post->ID
    );

    $actions['duplicate'] = '<a href="' . esc_url( $url ) . '">Duplicate</a>';

    return $actions;
}
add_filter( 'post_row_actions', 'custom_add_duplicate_post_link', 10, 2 );

function custom_duplicate_post_handler() {
    $post_id = isset( $_GET['post'] ) ? absint( $_GET['post'] ) : 0;

    check_admin_referer( 'custom_duplicate_post_' . $post_id );

    if ( ! current_user_can( 'edit_post', $post_id ) ) {
        wp_die( 'You are not allowed to duplicate this post.' );
    }

    $post = get_post( $post_id );

    if ( ! $post || 'trash' === $post->post_status ) {
        wp_die( 'Invalid post.' );
    }

    $new_post_id = wp_insert_post(
        array(
            'post_title'   => $post->post_title . ' (Copy)',
            'post_content' => $post->post_content,
            'post_excerpt' => $post->post_excerpt,
            'post_status'  => 'draft',
            'post_type'    => $post->post_type,
            'post_author'  => get_current_user_id(),
        ),
        true
    );

    if ( is_wp_error( $new_post_id ) ) {
        wp_die( esc_html( $new_post_id->get_error_message() ) );
    }

    wp_safe_redirect( admin_url( 'post.php?action=edit&post=' . $new_post_id ) );
    exit;
}
add_action( 'admin_post_custom_duplicate_post', 'custom_duplicate_post_handler' );