I built this for myself some years ago and used it a lot to find many interesting niche subreddits. Today I expanded it to also help myself and others find interesting niche communities across the Lemmyverse!
It will (try to) find everywhere it has been shared on the Lemmyverse (and other websites)
It will show you all comments from everywhere it's been shared on a single page
You can do all the regular stuff like filter, sort, isolate etc.
One thing I find myself doing very often is hitting "toggle sources" on the top banner; this shows me everywhere the link has been shared and commented on, and if I see a community I'm not familiar with, I'll isolate the comments from that source and have a look through to see if it's a community I'd like to engage with.
There are also browser extensions and an iOS shortcut available.