In my experience, those either get detected(?) and let through (rss can be agressively cached after all) or you're out of luck and the website owner set up e.g.

In my experience, those either get detected(?) and let through (rss can be agressively cached after all) or you're out of luck and the website owner set up e.g. wordpress (which automatically included rss URLs) but did not configure cloudflare to let rss through.