Apple hasn’t really paid much attention to its Books app, although Books finally got thrown a wee bit of a bone interface wise in ios16. Audiobooks is a key area it is has not been given any love. Basically you have to buy an audiblebook at exorbitant prices (AUD$30 plus) in the Books app.
There are some books available through the podcast app, but it is pretty limited.
Over on kindle, if you buy a kindle book for an extra couple of dollars if an audio version exists for many books. And there is also the classic audible subscription (Amazon owns audible) but it is not good value of money and an area ripe for classic disruption. I would also note that all Apple Books has over The Kindle App is you can buy books directly in the app, whereas Apple requires the buyer to go outside the app to a browser for kindle. Bad Apple.
I would expect the spotify effort is more like the Apple podcast, but specifically given development attention and promotion to help spotify diversify. Meanwhile, Apple Books in general, and thus audible books as well, has been on the back burner at Apple for sometime. It was clearly burnt badly in that antitrust case, and went into classic avoidance. Meanwhile Amazon won all it desired, ironically reduced competition for kindle.
I still believe the digital book market is ripe for disruption, including audiobooks, and Apple is just about the only company that can do it. Maybe Spotify can do it if Apple isn’t willing to go to the effort.
On the other hand, the Books app is really neat for reading epubs purloined elsewhere