I've searched for a question on this and cannot find anything. I'm sure there must be one, but if so we'll dupe this and create a better signpost to it.
Currently the search function in the Help Center is entirely broken. No results are returned regardless of what is searched for.
This seems to be on all sites, certainly the ones I tried.
Examples using "ask" as the search keyword, as this should most certainly return results (links go directly to each site's help center->search with keyword "ask"):