Currently on Special:Search on Wikidata, only the search in the main namespace and property namespace is enabled by default.
As a user looking for a Lexeme (or Form or Sense) if I type the word I look for in the search field, I find nothing. I need to change manually the namespace of the search, or add Lexeme: or L: as a prefix. This is not very intuitive for users, especially new users.
Looking by default for items and Lexemes should be allowed in Special:Search and the search bar.