I was going to say... Mac OS / iOS user here. I joined 2 months ago. The extension has worked flawlessly for me - glad you found out the new extension worked!
Steps I took: I installed the extension - activated it in Safari Extensions. Then I went to duckduckgo.com - and gave the extension full access ONLY to DuckDuckGo.com. I set my search engine to duckduckgo in safari. Bam, good to go. Been doing this for 2 months with 0 problems now.
This has been working perfectly on my iPad, Mac, and iPhone.
The new app on iOS is kinda just informative - has a video of what you need to do (above steps visually).
Also submitting Apple feedback for Kagi 😃.