Did you happen to figure this out? I'm having the same issue.

This is basic functionality. It's really surprising/embarrassing that all major libraries out there have this functionality built in but the official Apple library MusicKit doesnt provide a simple method to capture the data to create a sound wave chart..

I am a huge fan of Apple since 2000 but the quality of the software has been degrading lately at a faster rate. Apple software was known for being extremely stable with almost no errors. but now we see constants errors, buggy software, and unnecessarily hard steps for simple tasks. Please do not become Microsoft..