<?php

function my_facetwp_is_main_query( $is_main_query, $query ) {
    if ( isset( $query->query_vars['facetwp'] ) ) {
        return (bool) $this->query_vars['facetwp'];
    }
    return false;
}
add_filter( 'facetwp_is_main_query', 'my_facetwp_is_main_query', 10, 2 );