In Safari, tap Share, then RectoVerso. Choose the kind of cards and how many, and tap Make 20 cards (or the number you chose). Then open RectoVerso: the deck maker is already writing, and every card waits for you to check it. If RectoVerso’s notifications are on, tapping the one that comes opens it too.
The same works for text you select in any app, a text file or a PDF (share it from Files). A link on its own isn’t enough: open it in Safari and share the page. RectoVerso reads the page that’s already open, so it downloads nothing.
With Shortcuts instead: in the Shortcuts app, add Get Article using Safari Reader (input: Safari web pages), then Make a Deck (RectoVerso), with the article’s Body as its text.