I feel spoiled.
I greatly enjoyed the visualizer Ferromagnetic from the moment I discovered it, but I was cheeky enough to get in touch with the developer about some wishes for the app.
Now, Daniel Eke has gone and implemented everything (and more) I wanted.
First, the visualizer can now float behind other windows, acting much like a trippy wallpaper.
Second, the real killer feature: Ferromagnetic can now listen to and visualize system audio. After jumping through Apple's always scary-looking permission dialogs (which make complete sense for something you actually allow to listen to everything on your machine), it no longer matters if I play songs on Spotify, some random thing on Youtube, or even a podcast in Overcast - everything will be beautifully visualized.
Life is good.
(In the vein of "life is good"-news, I have now been on holiday long enough that I have started to be uncertain about which day of the week it is. I feel I accomplished this a lot quicker than average, setting a good bar to aim for in the future.)