It sounds simple on the surface. You copy a link on a site into a feed reader app. Then whenever that site updates you get a nice readable article on the app.
But that sounds like something that could be accomplished locally. Why does every RSS reader I run into require an account or otherwise rely on the cloud?
If you like RSS and have nextcloud setup, the news app has had a lot of love.
In short any RSS app that needs the cloud and an account, is an RSS aggregater. In that you sign up to the cloud site and can see the feeds on any devices that have an app.