The documentation is ambiguous, In the Help Book Registration section it gives two examples of how to register the help Book. First it says the <key>CFBundleHelpBookFolder</key> should be <string>SurfWriter.Help</string> then in the illustration it has it as Surf Writer Help. Then it has the <key>CFBundleHelpBookName</key> as <string>com.mycompany.surfwriter.help</string> but in the illustration it has it as Surf Writer Help. Which is it?
The help Book is still not searchable but I'll clear the cache with the terminal command: rm -rf ~/Library/Caches/com.apple.help* and see if it helps.
Like almost all of the Developer documentation the Apple Help Programming guide is not current and needs work.
Sorry if these questions have been asked before. The Developer Forums seem to be broken. No matter what I search for there are no previous posts.
There is nothing wrong with my help book. When I have problems like this one I tend to think it's my fault and re-read the documentation. My Help Book is configured correctly. The problem is that XCode 13, or more likely macOS Monterey 12.0.1 will only display the Help Book if the application bundle is in the Applications folder. So problem solved, sort of, you can't display the Help Book while debugging your Mac App in XCode. You have to archive it and export it to the Applications folder to see the Help Book. I can't update my application at the App Store anyway because of the infamous exit(173) bug in macOS Monterey.
Also the hiutil (Help Indexer app) does nothing in Monterey anyway so don't bother creating a help Index.