There are lots of ways you can use #RSS on the Fediverse:
-Follow any Mastodon account's public posts through RSS by putting .rss at the end of their profile URL. Use this address in your feed reader software.
-Follow any PeerTube account or channel by clicking the options menu next to the Subscribe button and selecting RSS.
-If you are on a Friendica server, you can use it as a feed reader. Paste an RSS feed address in the search box, that feed's posts will appear in your home timeline.
@feditips Is there an FOSS rss reader that syncs between devices without the need for self hosting? Feedly and Inoreader are the ones I generally use, but I really prioritize cross syncing between devices.
Friendica does that as you will see the same feed on whichever device you log in on. It's not a traditional RSS reader, but if you follow RSS feeds they appear in the Home timeline.
There's currently no dedicated Friendica app, but it works with the Mastodon API so Mastodon apps should work with Friendica accounts. I'm not sure how the Mastodon apps handle RSS follows though?