In the past, it was possible to sync (i)Books bookmarks, highlights, etc., through the cloud, without turning on iCloud Drive for the Books app, or uploading personal epubs (not purchased from Apple) to iCloud Drive. Has this been removed from iOS?
Using iOS 9.3.6 for example, it was possible to do this by turning on Settings > iBooks > Sync Bookmarks and Notes, and Sync Collections, while having Settings > iCloud > iCloud Drive > iBooks turned off. Books were not uploaded to iCloud Drive. The highlights etc. were synced using the Apple ID used for iTunes/AppStore/iBooks purchases, which is not necessarily the same as the Apple ID used for iCloud. Books could be synced from the Mac with a cable, with Books disabled in iCloud Drive. The Mac's Books Preferences > General > Sync: "Sync collections, bookmarks and highlights" is checked, and highlights and bookmarks were synced through the cloud, in real time.
I got a new device with iOS 15, and there is only Settings > Books > iCloud Drive, and Reading Now. Below this, it says "To enable syncing across devices, sign in to iCloud and turn on iCloud Drive in Settings". I haven't done that, but I think it will trigger the books that I synced with a cable from the Mac, to be uploaded to iCloud Drive, which I don't want. But I can't see how to get the highlights and bookmarks to sync without that - none of the books on the new device have their bookmarks.
Using iOS 9.3.6 for example, it was possible to do this by turning on Settings > iBooks > Sync Bookmarks and Notes, and Sync Collections, while having Settings > iCloud > iCloud Drive > iBooks turned off. Books were not uploaded to iCloud Drive. The highlights etc. were synced using the Apple ID used for iTunes/AppStore/iBooks purchases, which is not necessarily the same as the Apple ID used for iCloud. Books could be synced from the Mac with a cable, with Books disabled in iCloud Drive. The Mac's Books Preferences > General > Sync: "Sync collections, bookmarks and highlights" is checked, and highlights and bookmarks were synced through the cloud, in real time.
I got a new device with iOS 15, and there is only Settings > Books > iCloud Drive, and Reading Now. Below this, it says "To enable syncing across devices, sign in to iCloud and turn on iCloud Drive in Settings". I haven't done that, but I think it will trigger the books that I synced with a cable from the Mac, to be uploaded to iCloud Drive, which I don't want. But I can't see how to get the highlights and bookmarks to sync without that - none of the books on the new device have their bookmarks.