Some types of Fediverse servers let you follow their accounts through RSS newsreader apps.
On Mastodon, you can follow any account through RSS by going to the account’s original page and adding .rss to the end of it. For example, the RSS feed for the FediTips account is https://email@example.com ⧉. Note that this only shows public posts, you will not see replies or followers-only posts on the feed.
On PeerTube, you can follow any account or channel through RSS by going to its page and clicking the Subscribe button, there will be an RSS subscription option at the bottom of the menu. You may also see RSS logos next to various features that give you RSS feeds for those features.