For my own web-based RSS reader I made no effort to open stories in an <iframe> or anything like that but I just show the text in the RSS feed and if I want to see the article I click on a link an it opens a new browser tab.
I've been arguing with people since 1994 that staying within the bounds of the web gave you more freedom then it takes away. My RSS reader works w/ my iPad and my VR headset.
For a while I have been thinking people haven't demanded more transclusion capability from the WWW, like you ought to be able to merge the DOM from a web site into another page. I did two projects in the 2010s, one to see what was possible in terms of transclusion of pure-HTML pages and another "de-enshittification" project which would re-render JS-based pages as the DOM level the way Google's web crawler (or maybe archive.is) but a week's spike prototype on that one convinced me that it made latency, arguably the core problem of enshittification, much much worse. On the other hand for an RSS reader you could do the work up front.
