Ah, my bad! I should have guessed by your username, which I assume is in reference to the now-defunct reddit app.
I can't personally vouch for it, but NetNewsWire might be a good option for iOS if you haven't tried it. It's also FOSS, updated as recently as June 2023, can read RSS feeds locally and has a reader view to fetch full articles. You'd have to test if it caches fetched articles though, but I don't see why it shouldn't.