Field type "POST" that returns post of a custom type created by the same user

Hello,

You can use the code to register the field and get the current user then assign it to the setting query_args. For example:

add_filter( 'rwmb_meta_boxes', 'callback_function' );

function callback_function( $meta_boxes ) {
    $current_user_id = get_current_user_id();
    
    $meta_boxes[] = [
        'title'      => __( 'My Custom Fields', 'your-text-domain' ),
        'id'         => 'my_custom_fields',
        'post_types' => ['post'],
        'fields'     => [
            [
                'id'         => 'funnel_post',
                'title'      => 'Funnel Post',
                'type'       => 'post',
                'post_type'  => 'funnel',
                'query_args' => [
                    'author' => $current_user_id,
                ],
            ],
        ],
    ];

    return $meta_boxes;
}

Refer documentation https://docs.metabox.io/fields/post/
https://developer.wordpress.org/reference/classes/wp_query/#author-parameters