only 1 category

add_filter('the_category_list',function ($categories){
    $main_cat = jnews_get_primary_category( get_post()->ID );
    if ( $main_cat ) {
        return [get_category($main_cat)];
    }
    if ( ! empty( $categories ) ) {
        return [$categories[0]];
    }
    return $categories;
});