Discussions about how to ID unknowns come up fairly regularly in the forums actually (if you do a search for “unknown” you will discover a bewildering number of threads), and usually there ends up being some interesting and useful info in one comment or another, which of course inevitably eventually gets lost in the pile of new threads.
This one may be a good starting point: https://forum.inaturalist.org/t/good-global-criteria-when-identifying-unknowns/47167/7
So again, it seems like it is a findability issue for information that is scattered unsystematically in many places, rather than there not being any information.
There are some resources collected in this observing wildlife wiki, though I’m not sure how much it gets looked at/updated.
I wonder if it would make sense to use one or more of the “unknown” projects (e.g., @bobmcd’s “state of matter life” project or @jeanphilippeb’s yellow projects) as a place to collect resources and tips for IDing unknowns and narrowing broad IDs. Generally project creators and anyone they have named as an administrator can create journal posts, so it would require some coordination between project creators and anyone who is interested in contributing content.
(The reason I keep pushing the idea of journal posts here is because it seems like a better way than forum posts to ensure that relevant information remains accessible for those who want to refer to it – if you join a project any associated journal posts are essentially bookmarked for you and you can get updates if new journal entries are posted.)