@MB
I looked at the search code and can see that it's only title and description that are considered, but please look again at the screenshot!
Listing title is Mercedes. Search is for mercedes and this was using full-text search with NLP in current locale. Listing is in English, search is in English.
Search desperately needs an overhaul ... Mysql full-text search can do more if integrating an open source search solution, and there are many good ones, is not on the roadmap. This is so much more important than adding ancillary plugins and features.
Also, why add "Add to search engine" option in Attributes plugin if they're not even being considered in search? The whole idea behind a classifieds platform is to find and list items, services etc. and if users aren't able to find listed things then purpose or idea goes out of the window.
For example - Mercedes was listed using the body style attribute "Coupe" but this attribute was not used in the title or description of the listed item. Anyone searching for coupe, won't find the mercedes or all coupe cars listed!
To avoid any confusion, there's no search engine here. Just plain mysql full-text search on 2 fields, title and description, that isn't properly working.
A search engine is something like elasticsearch, sphinx, typesense, manticore etc.