Netflix audio is available as unencrypted .aac files with no protection whatsoever. Netflix doesn’t use widevine for anything except video.

Here's a typical media manifest for a typical piece of netflix content: https://gist.githubusercontent.com/justjanne/b2cbff54588466f... (identifying data and URLs redacted).

Note how (a) the audio is only 128kbps, and (b) the audio is just directly linked (the files are just aac directly, you can play them in any player).