i lost all my books after updating 12,

Restore them from your Time Machine backup.

They are located here:

~/Library/Containers/com.apple.BKAgentService/Data/Documents/iBooks

the ~ is your user.

You Enter Time Machine and the at a time right before you upgraded go to their and select the books and restore them NOTE that the books only have alphanumeric titles.

I found the location from here:

https://www.idownloadblog.com/2018/05/24/ibooks-library-location-mac/

and verified it is the correct location for Monterey.

Hey karel215,

It sounds like you're missing books from your Mac after updating. We can understand wanting to look into that further. We want to help.

We'd recommend reviewing the steps in this article: See your books and audiobooks on all your devices with Books on Mac

Thanks!