Has the boolean search option been removed in the latest version?

I'm not aware of any product changes that would cause this to happen. Boolean search is not available if the vault is using Smart Search as the search engine, have you perhaps taken a new search engine in use recently? If not and you believe this is a product issue, please raise this with M-Files Support for investigation.

Thank you Joonas Linkola we moved to SmartSearch a while back but are just updating our training documentation now which is why we have noticed it has gone! 

Thank you Joonas Linkola we moved to SmartSearch a while back but are just updating our training documentation now which is why we have noticed it has gone!