I reformatted my Mac and wanted to sync some books and ran into the same issue.
This time I just did what you suggested - iCloud > iCloud Drive > Books enabled (and the equivalent on my iOS devices) but when I double click an ePub file, it opens in Books, but it does not then automatically transfer to my iPad or iPhone
What I have to do instead is Airdrop the epub file on to the iPad. Once it’s on the iPad the syncing of highlights etc work fine - so if I highlight a paragraph on the iPad it will show highlighted on the book on the Mac (and from Mac to iPad). But it doesn’t seem to automatically copy the books onto the other devices, is that how it works for you too @Hallski?
(I would have thought that just opening a file in the Books app on any device would automatically copy it to others synced vis iCloud)
I’ve just been on to the phone to them for the last few hours and unfortunately everything they suggested did not work. However just as they were about to escalate things to an engineer I thought I would uninstall Little Snitch to see if that helped (previously I had disabled network filter while troubleshooting) so I uninstalled it, tried again but no joy
But then I installed it again, and also logged out of iCloud and back in again. Well this time Little Snitch asked me to allow Cloudd to connect to Google’s servers (I know for a fact that last time I clicked deny) so this time I clicked allow… and it all works now! I now need to simply open an epub in Books on my Mac and it automatically transfers to all my iOS devices
So here’s what I think happened:
I denied the Cloudd service to connect to Google’s servers via Little Snitch
That got logged or associated with my iCloud account or got stuck in some sort of loop
Then logging out of iCloud and back in again re-triggered the connection which re-triggered the request in Little Snitch.
I’m just glad it’s all working now!
Thanks for your help @Hallski - if it wasn’t for you I might have thought I had to keep connecting my devices via cable or airdropping to transfer them over!