I searched 'kagi fediverse lens' and landed on a thread with people discussing Mastadon functionality. It isn't clear to me what the lens is, but it sounds like it's a search tool for specifically fediverse sites? What's the functionality of it? I'm kinda curious about testing it out.
Kagi is a search engine and when you start a search you can enable different lenses, which are like filters that only show you results from that category. The fediverse lens shows you results from Lemmy and other fediverse instance, the forums lens shows results from a wider collections of forums only sites, etc
I discontinued my subscription because it's stupidly expensive and they keep investing in dumb AI shit I don't want rather than making search cheaper and/or better.
Gotta admit, I do miss it. It's a neat service. But not for that price.