Exclude Categories from RSS Feed

Insert the code snippet into your theme’s functions.php, a helper file, or a functionality plugin to exclude specific categories from being displayed in WordPress RSS Feed results.

X where X is the number/ID of your category, comma separated for multiple

function myFeedExcluder($query) {
if ($query->is_feed) {
   $query->set('cat','-X');
   }
return $query;
   }
add_filter('pre_get_posts','myFeedExcluder');