How can I access collections in the Books app on macOS 26?

Can anyone tell me where 'Collections' have gone in OSX 26 Tahoe. You can still add a particular book to a specific 'collection', but you cannot access the 'Collections' themselves. This is extremely irritating for those of us who have gone to the trouble of organising our books into specific 'collections'!

[Re-Titled by Moderator]

Original Title: 'Books' app in OSX 26 Tahoe