I'm not sure about the "audiobooks" part but you can use your browser from android to connect to calibre https://manual.calibre-ebook.com/faq.html#over-the-air

BTW I used for many years Moon+ Reader to read aloud my ebook on android. Not quite as a real audiobook but good enough https://play.google.com/store/apps/details?id=com.flyersoft.moonreader

If you are able to see every recipe I'd rule out data corruption. If the issue arise only when try to create a new recipe (or editing an old one) the usual thing to check are permissions. Don't zip but use some tools to maintain permissions (tar, rsync, etc) and try again

It really depends. I usually prefer json. It’s easily understandable from humans and from machines, it doesn’t depends on indentation and above everything else I like it very much 🤣