Vaguely related, I did an extremely basic RSS feed combiner ages ago: https://hn-blogs.kronis.dev/ when there was that one post where people could share their blogs and many of those had RSS feeds.

That said, it got its list of feeds from the repo that someone made which hasn't been updated in a few years, so even if new blog content gets pulled, the list of blogs doesn't change. Oh well, wasn't a super serious project.