exclude posts from blog and feed

Hi,

in my child theme’s functions.php I tried to apply a filter to hide certain posts that belong to a travel guide I’m working on, I tried to use this code here:

function excludeMetaKey($query) {

  if ( $query->is_home && $query->is_feed && $query->is_main_query() ) {

      $query->set('meta_key=mappress&meta_value=ns');
   }
return $query;
}

add_filter('pre_get_posts', 'excludeMetaKey');

Unfortunately it is not working.
Any hints what I’m doing wrong?

Many thanks in advance.
Cheers
Yogie