Actually, the documentation does not make it better. Why does it confuse MIDI stuff (simple/advanced) with offline processing. The answer here: [Solved] Direct offline processing problem (Cubase 9.5) - Developer / VST 3 SDK - Steinberg Forums makes it even weirder. And offline processing is actually declared in setupProcessing(). So does a complex plugin then get two setIoMode() calls, one for advanced and one for offline processing (which is probably that Cubase Function “Direct Offline Processing”)?