On our installation the enable button for CMS search mentioned in docs doesn't show up This is what works. We know it is evil to hack modules directly

<?php
/**
 * Searches the contents of native cms pages.
 *
 * @package OFFLINE\SiteSearch\Classes\Providers
 */
class CmsPagesResultsProvider extends ResultsProvider
{
    /**
     * Runs the search for this provider.
     *
     * @return ResultsProvider
     */
    public function search()
    {
        if ( ! $this->isEnabled()) {
            //return $this; <== Comment this !
        }