You should have a template books/list.html with your logic there to list the items in your books directory. If you don’t have that template, Hugo will use the _default/list.html template. Otherwise, it would be easier to help you if you posted your repo.
I think I have made some progress, I didn’t have a baseof.html . I have put this in and it displays the list as expected. Is this what we would expect as the docs don’t mention it?
Not sure, tbh. It’s better to have a baseof file than not, but I don’t know the effect of not having it (having never tried not using one). Glad you made some progress!