A while back I built a site that converts RSS feeds to ActivityPub actors that you can subscribe to from Mastodon and other ActivityPub-compliant social networks: https://bots.tinysubversions.com/convert/
I've now also published the source code: https://github.com/dariusk/activtypub-to-rss
@darius So f-ing cool. Thank you!
Revel in the marvels of the universe.