How to exclude a certain category?

Hi there,

i would like to exclude a certain category from displaying, search etc.
i already tried this well-known version in the functions.php – only getting several warnings/failures:

function exclude_category_posts( $query ) {
if ( $query->is_home() && $query->is_main_query() ) {
$query->set( ‘cat’, ‘-7’ );
}
}
add_action( ‘pre_get_posts’, ‘exclude_category_posts’ );

`

i even tried the UCE-plugIn which didn’t worked either – every category was excluded!

So please – it would be very kind, if you show me how to do it

best regards