Darius Kazemi, the creator of Hometown, made an AP server where you can register a feed and it turns into an actor (ie an account): https://github.com/dariusk/rss-to-activitypub

I made my own thing, fetching an RSS feed and posting entries to an existing account. It makes the code much simpler, but is not practical if you have lots of feeds (you need yo create all accounts separately): https://sr.ht/~rakoo/rss2ap/