Hi, and thanks for working on this module!
This is related to 🐛 Book navigation title override doesn't work with custom book block Active which describes a different but related setting.
However, there is also this setting:
Show top level item
Enable this option to display the first page in the book with all other pages displayed below it.
This is not respected in the code it seems, so there is no way to show the first page in the book at all, if you decide to show the block only on book pages. If you show it on all pages, it does render the full tree. The code will only render items below the top page.
Active
2.0
Code