save new post by cmb2_get_metabox_form on frontpage

hi,

is it possible to create a new post from a custom metabox?
I’m getting the metabox form by the function cmb2_get_metabox_form

The form is shown on frontpage, but i can only edit a post and not create a new post

Code below:

//create shortcode
class CustomFrontendform {

    public static function init() {
        add_shortcode( 'cmb-form', array( __CLASS__, '_do_frontend_form_shortcode' ) );
    }

    public static function _do_frontend_form_shortcode( $atts = array() ) {

        // If no metabox id is set, yell about it
        if ( empty( $atts['id'] ) ) {
            return 'Please add an "id" attribute to specify the CMB2 form to display.';
        }

        $metabox_id = esc_attr( $atts['id'] );
        // Get our form
        $form = cmb2_get_metabox_form( $metabox_id );

        return $form;
    }
}

new CustomFrontendform();

// custom metabox
protected function hooks() {
        add_action( 'cmb2_init', array( __CLASS__, '_register_custommetabox_formfields' ) );
    }

    /**
     * custommetabox field
     * Hook in and add a metabox to select templates
     */
    public function _register_custommetabox_formfields() {
        new_cmb2_box( array(
            'id'           => Bootstrap::PREFIX . 'custommetabox',
            'title'        => __( 'Kleinanzeige', 'cmb2' ),
            'object_types' => array( 'custom_posts', ), // Post type
            'cmb_styles'   => false,
            'fields'       => array(
                array(
                    'name' => __( 'Email', 'cmb2' ),
                    'id'   => Bootstrap::PREFIX . 'email',
                    'type' => 'text_email',
                ),
                array(
                    'name' => __( 'Phone', 'cmb2' ),
                    'id'   => Bootstrap::PREFIX . 'phone',
                    'type' => 'text',
                ),
                array(
                    'name'       => __( 'ZIP', 'theme-domain' ),
                    'id'         => Bootstrap::PREFIX . 'zipcode',
                    'type'       => 'text',
                    'attributes' => array(
                        'type' => 'number',
                    ),
                ),
                array(
                    'name'         => __( 'Image', 'cmb2' ),
                    'id'           => Bootstrap::PREFIX . 'image',
                    'type'         => 'file',
                    'preview_size' => array( 100, 100 ),
                ),
                array(
                    'name'    => __( 'Text', 'cmb2' ),
                    'id'      => Bootstrap::PREFIX . 'content',
                    'type'    => 'textarea',
                    'options' => array(
                        'textarea_rows' => 12,
                    )
                ),
            )
        ) );
    }

https://www.ads-software.com/plugins/cmb2/