There is no such thing as keyword search with the search bar. It searches literal. The titles, devloper names and sometimes the short description tagline if there are not enough results. Results are capped in search at about 60.
There is tag browsing. That's not a search. You just display all games that have that tag. Those are sorted by popularity by default. So you would use your keywords as tags.
https://itch.io/games/tag-dungeon
https://itch.io/games/tag-troll
But beware, those tags might not be used the way you think they are. Seek similar games on Itch and have a look what tags they use.