Use post field with meta_query

Hello, how can I use the post field to look up words in a specific key instead of just title
(meta_query = key )

// Register meta boxes and fields for settings page
add_filter( 'rwmb_meta_boxes', function ( $meta_boxes ) {
    $meta_boxes[] = array(
        'id'             => 'general',
        'title'          => 'Default Domain',
        'settings_pages' => 'ims-core-trades-settings-domain',
        'tab'            => 'general',
        'fields' => array(
            array(
                'id' => 'url_1',
                'type' => 'url',
                'name' => esc_html__( 'URL', 'metabox-online-generator' ),
            ),
            array(
                'id' => 'post_2',
                'type' => 'post',
                'name' => esc_html__( 'Post', 'metabox-online-generator' ),
                'post_type' => 'domain',
                'field_type' => 'select_advanced',
                'query_args'  => array(
                    'post_status'    => 'publish',
                    'posts_per_page' => - 1,

                    'meta_query' => array(
                        'relation' => 'AND',
                          array(
                         'key' => 'domain_mf_default_url',
                         'value' => searched word,<-----------
                         'compare' => '=',
                         ),
                     
                     )

                ),
            ),
        ),
    );
    return $meta_boxes;
} );