You can try #Freerse. Freerse has a long article reading area. The profile also has a menu bar for articles. You can also post long articles directly. Long articles are displayed in the feed as cards.
https://image.nostr.build/35dc5c0df3be7ef354672038897567ec572cc3dd573dbad923ce772c49d8fa42.jpg
https://image.nostr.build/9e3cc6a98954902eb84cb9f311f990d73a267d4e2eb7a8a43ca2eadb98022d3c.jpg
https://image.nostr.build/a50686a190900e5c368adc1391bec39873f9df0d55760f08dfa4fc4c3560561f.jpg 

 Nice!
Is it opensource?
In the repo (https://github.com/Freerse/Freerse) I can just find the apk. 

 Yes, many users want to install APK, we provide an installation path. Freerse is not open source yet