Using InDesign 2022 Prerelease (17.0.0.96).

When I opened my Book file, created with the current released version (16.4.0.54), in this new version, it wouldn't let me hit ⌘S to save.

It keeps prompting me to save the file anew, as though it had just converted it fresh or created the Book.

The world is not going to stop revolving around its axis over this one, but it was disconcerting and annoying.