Adding a question mark to a currency conversion query disables Kagi Knowledge and enables Quick Answer. However, Kagi Knowledge provides accurate and current currency exchange rates, but Quick Answer inevitably relies on outdated information. Sometimes it confidently says "Today, the exchange rate is [oudated rate from a few days ago]" and sometimes it discusses various sources and hypothesises that the most recent one is probably the most accurate.

I think most users entering currency conversion queries are looking for current exchange rates, so I would recommend disabling Quick Answers for this type of query, or at least also enabling Kagi Knowledge.