Exclude Categories from Search in WordPress

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 search results. Apply the following code snippet to your theme’s functions.php, included helper functions, or a functionality plugin.

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

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