Relevanssi – disable FacetWP for the search archive

<?php

add_filter( 'facetwp_is_main_query', function( $is_main_query, $query ) {
    if ( $query->is_search() && ! empty( $query->get( 's' ) ) ) {
        $is_main_query = false;
    }
    return $is_main_query;
}, 8, 2 );