Read WordPress search special characters for more information.
The problem with special characters (including apostrophes) that some of them have many different visual variations. For example apostrophe characters ‘, ’ and ‘ are 3 different ones. When making a search query, the database treats these characters separately. If the correct one is entered, it will match, otherwise, it won’t.
Add a site search to your website that supports special characters
Support for special characters comes with advanced search features supported by third parties like ExpertRec.