Reckons Team Google Custom Search can be used, if you made these litle 3 changes:
1. In Xenforo ACP, open the Template: rtGCS_search_google_results
... and
replace all in it with this code:
HTML:
<li id="google_results">
<script>
(function() {
var cx = 'XXX';
var gcse = document.createElement('script');
gcse.type = 'text/javascript';
gcse.async = true;
gcse.src = 'https://cse.google.com/cse.js?cx=' + cx;
var s = document.getElementsByTagName('script')[0];
s.parentNode.insertBefore(gcse, s);
})();
</script>
<gcse:searchresults-only></gcse:searchresults-only>
</li>
2. Replace the XXX (line 4) with your Google Custom Search Engine ID,
but leave the ' ' at there place at beginnig and at the end of the ID.
3. Now you go to: https://cse.google.com/cse/search and change under "Design" from "Overlay to "Results only":
View attachment 164727
Thats all, and the Add-on works like bevor Dezember 2017.
Vor me, with a Xenforo 1.5.15 it works as just bevor - so enjoy to made it also working again.