After upgrading to Monterey I found that the Help system wasn't displaying my Help Books. After wasting an hour or so I figured out the the Help system will not display a Help Book unless the app was launched from the Applications folder. So, if you're launching the app from Xcode the Help Book won't work. If you want to see if the Help Book is properly configured you have to dig into the project's DerivedData folder, drag the app to the Applications folder and launch it from there.
Help Books not working
SOB! I've been trying to debug this on many catalyst apps for months - many thanks to you. What I do to see the help book is archive the maccat app, then export using the Copy option, then drag that copy to Applications. This is required for every change to the help book.
While I'm ranting about recent maccat changes, you can no longer use Credits.html for your About box info, that file must now be rich text Credits.rtf.