Try to open a provided book, get an error similar to this :
Open book c:/Program Files/Azure Data Studio - Insiders/resources/app/extensions/Microsoft.sqlservernotebook/c:/Program Files/Azure Data Studio - Insiders/resources/app/extensions/Microsoft.sqlservernotebook/c:/Program Files/Azure Data Studio - Insiders/resources/app/extensions/Microsoft.sqlservernotebook/books/sqlserver2019 failed: Failed to find a Table of Contents file in the specified book.
Insiders/Main
Try to open a provided book, get an error similar to this :