Why is there no "Avalable Now" feature/ option on the new format for Audiobooks anymore?
If you are using the Libby App, you can set Availability under your preferences. When searching, click on the red button with a + sign. The first filter listed is Availability, you can set to Available Titles or Everything. Here are more detailed instructions from the Libby App Help on Searching & Filtering.
You can also set the Libby App to just display audiobooks if that is your preference.
If this doesn't answer you question, please let me know.