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.