I was trying to use Advanced Search. In the field "all these words" I input: C#, in the field "this exact word or phrase" I input: "detect a key press" "during printing", I left the fields "any of these words" and "none of these words" blank. I left the "Then narrow your results by..." category with default values — which are shown in a screenshot.

Category with default values.

The first part of the advanced search, for easier readability.
After pressing the Build search button the search query was C; the search link was https://kagi.com/search?q=C#%20%22detect%20a%20key%20press%20during%20printing%22. It appears the # symbol is not correctly escaped and so the search result is incorrect.

Search query and results

Search URI
I expected Kagi Advanced search to search for results that contain the word C# and the phrases "detect a key press" and "during printing".