There are some visualizers in the Mac App Store. I'm using Ferromagnetic right now and like it well enough. There are still visualizers in Apple Music left over from the iTunes days but they're kind of lame.
I stumbled onto one years ago by accident, maybe an Easter egg or something. I came back to my computer (Mac) after several hours of iTunes playback to see a hitherto unknown visualization running, with fairly primitive-looking graphics by today's standards. It was not any of the visualizations available in iTunes at the time.
I filed a bug on it with Apple and they got back to me asking how the hell I had invoked this, because they'd never seen it before. Never did get to the bottom of it.
