I’m fairly certain Apple Music makes pretty heavy use of webviews.

Actually it does not. It used to, but then was rewritten. The Accessibility Inspector app can be used to see what's the class of the UI elements, if you want to check.

I think it still might. I use it all the time on my laptop, and periodically if I do something funky with the network, the entire view panel says that there was an internal server error in that classic no-CSS Times New Roman font. Do you have a source for this?

As I wrote above, use Accessibility Inspector to inspect the UI.