Mix mic and system audio to speakers on macOS?

question on Audio mixing and routing: mixing microphone and system audio and output to speaker?

On MacOS, is there any way to mix the audio input from an input

device, say a USB microphone, with the system sound output (say from a

video player) and send the combined audio stream to the sound output

device (speaker or a headphone)?

I tried in Audio MIDI app to create aggregated device combining

the USB input and system sound, and to set the aggregated device as the

system input, but upon output only the audio from the video player is

heard.