My iTunes (currently 18.104.22.168) consumes ~25-30% CPU whenever I listen to any music.
The only trick I found to resolve this is to switch it to the “Miniplayer mode”, e.g. using
Ctrl+Shift+M keyboard shortcut (use the same shortcut to switch back).
It has to be a weird glitch in iTunes, but the CPU usage almost immediately drops to 1-2% CPU.