According to this article https://support.apple.com/en-ca/guide/audio-midi-setup/ams59f301fda/mac
I should be able to use my iOS device connected via usb as a sound input.
But when I follow the instruction the input is shown and I have even enabled it, the bars are even moving but no sound is heard on the mac.
Best Answer
You need first something to capture the input, which can then be routed to an output.
Launch Quicktime Player, elect New Audio Recording & next to the red dot, select your input.
Turn up the volume slider underneath.
This should then route to your outputs, allowing playback. You don't even need to start the recording.
There will be latency, maybe as much as half a second.