It depends on what type of field the “featured portfolio” field is, you say checkbox, does that mean a true false field?
You need a field that is sortable. A true false field stores a 0 or 1, so it is sortable.
'meta_query' => array(
'featured_clause' => array(
'key' => 'field_name',
'compare' => 'EXISTS'
)
),
// order by featured clause descending, true will be shown first
'orderby' => array('featured_clause' => 'DESC', 'date' => 'DESC')
