I maintain a similar index-of-indexes but it's intentionally non-curated, restricted to indexes that use the OPML format, and uses autodiscovery to expand the list. The site needs some work, but it's up to 356 indexes.
https://blogroll-network.alexsci.com/blogrolls/
I'd recommend looking at anything with "planet" in the name, there are a bunch of tech communities that manage community feeds and they are high quality. There are also a ton of personal blogroll recommendations via micro.blog too.
Another index-of-indexes is https://brisray.com/web/webring-list.htm, which tracks 648 webrings!
And https://brisray.com/web/indiedirs.htm, which has some other great indieweb indexes
Now we need an index of indexes of indexes. I too keep such a list but it's just an Obsidian note I manually update
https://news.ycombinator.com/item?id=48089823
I also have a separate list of my favorite parts of the internet I plan to eventually turn into something like this: https://wilderness.land/ (my inspo)