I guess it would be more akin to a “source code hosting service,” but that would imply that I intend to open it to the internet (which isn’t necessarily the case).

For this website, it seems the only way is by fetching the MP3 URL from the network tab (or a random JavaScript file) and passing it into yt-dlp like so:

yt-dlp "https://audio.usborne.com/audio/Book Readings/Phonics Readers/9781801319591_pho_cockatoos-on-cruise_am-eng_br-pt.mp3"

This will correctly download it.