I have the Kagi extension on various iOS and MacOS devices making it the default search engine. It works well on all devices, except on an older MacBook Pro running MacOS 12.7.1 and Safari 17.1. I have it installed and after activating the 'default search engine' setting it forwards all my search queries to Kagi (with DuckDuckGo set as default engine in Safari). However, after a while (don't have a clear understanding what triggers it) Safari reverts to giving me DuckDuckGo results instead of forwarding to Kagi.
After disabling the Kagi extension and then enabling it again it works again. Until it no longer does after a while and the whole process repeats itself.
Always forward search queries to Kagi on older Mac & Safari versions.