Post type select

<?php
add_filter( 'rwmb_meta_boxes', 'your_prefix_register_meta_boxes' );

function your_prefix_register_meta_boxes( $meta_boxes ) {
    $prefix = '';

    $meta_boxes[] = array (
        'title' => esc_html__( 'Untitled Field Group', 'text-domain' ),
        'id' => 'untitled-field-group',
        'post_types' => array(
            0 => 'post',
        ),
        'context' => 'normal',
        'priority' => 'high',
        'fields' => array(
            array (
                'id' => $prefix . 'select_post_type',
                'name' => esc_html__( 'Post type', 'text-domain' ),
                'type' => 'select',
                'placeholder' => esc_html__( 'Select an Item', 'text-domain' ),
                'options' => array(
                    'book' => esc_html__( 'book', 'text-domain' ),
                    'author' => esc_html__( 'author', 'text-domain' ),
                    'post' => esc_html__( 'post', 'text-domain' ),
                    'page' => esc_html__( 'page', 'text-domain' ),
                ),
            ),
            array (
                'id' => $prefix . 'book',
                'type' => 'post',
                'name' => esc_html__( 'Book', 'text-domain' ),
                'post_type' => array(
                    0 => 'book',
                ),
                'field_type' => 'select_advanced',
                'visible' => array(
                    'when' => array(
                        array (
                            0 => 'select_post_type',
                            1 => '=',
                            2 => 'book',
                        ),
                    ),
                    'relation' => 'and',
                ),
            ),
            array (
                'id' => $prefix . 'post',
                'type' => 'post',
                'name' => esc_html__( 'Post', 'text-domain' ),
                'post_type' => array(
                    0 => 'post',
                ),
                'field_type' => 'select_advanced',
                'visible' => array(
                    'when' => array(
                        array (
                            0 => 'select_post_type',
                            1 => '=',
                            2 => 'post',
                        ),
                    ),
                    'relation' => 'and',
                ),
            ),
        ),
    );

    return $meta_boxes;
}