If you go to something like the For You screen, you will see a pause while the content is loaded remotely. And if you hit Command-R, it will reload, like a web

If you go to something like the For You screen, you will see a pause while the content is loaded remotely. And if you hit Command-R, it will reload, like a web page. I think the other commenters are right that Music.app is written as a native macOS app, but it definitely leans heavily on web views for content, especially in the streaming parts of the app.