Itch has two methods of "searching". One is literal title search. The other is browsing tags.
You do not search for keywords. There are no keywords. The title of the search box is kinda misleading in that it does not tell how it searches and that it claims to search "tags". But it does not search by tags, it searches in the suggested tag list.
If you enter a word in the search box and the word matches a "suggested" tag, those tags will appear above the results. The tags. Not games with that tag. The results will be literal title matches. And games whose developers are matching the search query. Results will be capped at around 60 results.
If you type a word in the tag box, it will browse all games that have that tag. A tag does not need to be in that list. Itch has freestyle tagging. But the search above only "searches" tags in that list.
https://itch.io/search?q=banana
https://itch.io/games/tag-banana
Genres are special tags. But as far as I can tell, for all intents and purposes, they are just tags that are named genre-something-something instead of tag-something-something. You can only select a genre as your main genre for a game. And they can be selected directly as genres, instead of using the tag box.
And one cannot do a title search within a filtered tag list. One can try using a regular internet search page. Itch pages are ranked high in relevance for indie games.