Here's a video of what my web app does in action: it lets me browse mangadex, select chapters of the manga I want, then it downloads the content and stitches them into an epub on the backend, then I can open it directly on the device using the native epub support, without having to reach for a computer. I'm quite pleased
https://nextcloud.chuckdries.com/s/8fYNDBT9Fq92NTe