Sort a custom post with ACF: Date Picker & Display Featured!

Please change your args like this.

$meta_query = array(
    array(
        'key' => 'event_type',
        'value' => 'featured',
        'compare' => '='
    )
);

$args = array(
    'post_type' => 'event',
    'posts_per_page' => -1,
    'order' => 'DESC',
    'orderby' => 'meta_value_num',
    'meta_key' => 'event_date',
    'meta_query' => $meta_query
);