Actually there are quite some app on hacker news now I aware of this. Just use safari and safe host page. Can export to pdf easier on top of login etc.
At some point, I built https://tefter.io/~hackernews so that I could read HN but also other feeds and keep them easily categorised and searchable. It's a progressive web app, so it's easy to install on most devices. Give it a try!
Personally I do not like feeds that take 1/2 page or more on my mobile to cover one item. Drawback of showing pictures for feed items.
HN is super nice because it is so condensed (for me).