It's pretty manual at this point. The indexing is done by hand. The idea is kind of crazy, but I think it can be made to work, in the same way that Wikipedia is maintained by hand.
https://digraph.app/
https://github.com/emwalker/digraph
If you can crowdsource the indexing, you get yourself a manually curated search engine with a nice topic graph that can be traversed. A piece of this puzzle that hasn't been tackled yet is a reputation system to keep the signal-to-noise ratio high and deal with spam.
> What’s an example use case of where you use that system to find a link?
An example use case is that I come across some interesting long-form article on a topic I'm following, e.g., Shackleton's expedition, that's published on a nice website and that I don't have time to read. I can just drop the link in the right topic and get back to it without too much difficulty. Or that's the hope, anyway. (Doesn't always work out that like that.)
Another thing I'm interested in is what the topic structure ends up looking like as it's more fully fleshed out. So sometimes I'll drop in random links even if they're not that interesting, just to build out the topics.