Is it possible to add any filters to the search result?

I see this topic but don’t understand how it can help me with this task…

Yes, Relevanssi supports most of the standard WordPress query parameters. If adding the parameter breaks the query, something’s wrong on your site, and it’s probably not caused by Relevanssi. How exactly is the query killed? What happens?

Oh, I think I found the answer to my question.

function filter_relevanssi_results($hits) {
    if (!empty($_GET['post_type'])) {
        $allowed_types = explode(',', $_GET['post_type']);
        $filtered_hits = [];

        foreach ($hits[0] as $post) {
            if (in_array(get_post_type($post->ID), $allowed_types, true)) {
                $filtered_hits[] = $post;
            }
        }

        $hits[0] = $filtered_hits;
    }

    return $hits;
}
add_filter('relevanssi_hits_filter', 'filter_relevanssi_results');

You can do it like that, but it would be much better to set the post_type parameter before the search so you don’t have to filter afterwards. It would be much more efficient that way. Relevanssi reads thepost_type parameter from $_GET, so this should just work without any extra hoops. It sounds like there’s a more fundamental problem on your site, and tackling that would be more efficient than fixing it with a patch like this.