Move to Book contrib module?

Yup.

IIRC, this was only developed because it was quicker than doing a patch for core, and back in the D7 days a new feature like this wouldn't have got in anyway.

I moved ✨ Allow access to page to order book page's children Needs review to the contrib module, marking this one done.

Automatically closed - issue fixed for 2 weeks with no activity.