Sorry for the delayed response.
There’s a solution for this use case. You need to create a song which include all of the tracks including the metronome as well. In the uTool you need to set up the proper mixer, so you need to mute all the tracks except the metronome, then export the song. With this setup you can hear only the metronome in the headphone but the device main outputs 1-16 will plays out all of the tracks.
I hope this helps