I have a related question about "Book with Link." I used this
feature in a subproject (Unity Code Reference) and it works fine.
But, because the Code Reference is so large, I decided to keep it
as a separate subproject and merge it with the main project (Unity
Software). When I compile the main project, I see the Unity Code
Reference book and all the topics, but clicking the book doesn't
bring up the default topic that I configured with "Book with
Link."