@ronald @chhopsky Just got a Satechi USB-C hub for my iPad Pro, which has USB A, C and headphone ports, and this was the device I needed to capture MIDI from my piano AND when using an iOS soft synth app, play back sounds out the headphone jack.
However, the iPad won’t let me select the heaphone jack as audio out, so my piano which can work as audio device and MIDI device steals both when connected. The trick is to not plug in the headphone until AFTER.