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.
Assuming you read RSS offline on mobile, Feeder has an option to fetch full articles and stores them for offline reading. It's FOSS and actively-maintained, having received an update just last week.
I've never encountered a site I wanted to follow that didn't have RSS, but I wholly agree it's often needlessly complicated to find the feed links.
I started using RSS during the summer. It filled a hole after I quit reddit, since I used to get a lot of my news from the subreddits for my city and my province. There's also the on-going bickering between Meta and Canadian lawmakers/news media groups which means I see way less articles on social media than I used to. Honestly, after adding a couple local news outlets to my RSS apps, I feel better informed than ever before, and I spend a lot less time arguing with people on reddit. Win-win if you ask me.
Anyone looking for good RSS readers, I use Feeder on my phone (Android-only), Fluent Reader on desktop (cross-platform), and I also use the RSS widget of the Renewed Tab addon for Firefox. Both apps I use work locally, and have the ability to fetch full articles in-app (the addon just opens the articles in Firefox).
Something also worth mentioning: you can often find RSS feeds by checking the page's source (on Firefox: right-click and "View Page Source") and using Ctrl+F to search, there's usually a URL somewhere. Keywords to search for: "feed", "RSS", "xml", "atom". For example, if I go to this community's page on lemmy.world, I can Ctrl+F "feed" on the page source to find https://lemmy.world/feeds/c/technology.xml
I think I've been more active on Lemmy in the past five days than I had been on reddit for the past 2 years.
Decentralization of social media is extremely enticing to me, and I really want this community to flourish, so I've been trying to make this into an active space.
Like I said, not an expert haha (thanks for explaining what mTLS is because I had assumed I knew but truly didn't)
That being said, I found a reddit thread detailing what seems to be the same issue as you, with OP linking a Stack Exchange post with their solution.