Probably already exists, but I couldn’t find anything, so made this… a shortcut for creating a direct link to an Audible audiobook. From Audible, share the book you want a link for to this shortcut. You’ll get an appropriate URL in your clipboard.
I use this in a workflow to maintain a list of audiobooks (Spotify and Audible), podcasts, ebooks, videos etc in progress via a GoodTask home screen widget that also serves as a launcher.