Each listing has a 3 dots menu which has the following options:
More results from this site
Remove results from this site
Open page in Web Archive
Summarize page
Ask questions about page
Would you consider adding another option:
Report page
The idea is for users to manually provide feedback as to why that page does not match the query. I realise this feedback would then have to be reviewed further to prevent abuse. But I think it would potentially be another way to refine your index?
For example, I searched for https://kagi.com/search?q=river+waveney with UK localisation turned on. The 4th result is "Conejos River" which is completely wrong, it doesn't have the word "waveney" anywhere on the page. Same goes for the 8th listing "Patuxent River" and several others. The Google results for this query are much better unfortunately.
User would report the page - not too much to add