Unfortunately, the headphone output on the Behringer is just an output.

I’ve been trying to think of a solution with minimal hassle/cost and I think this might be it …

Plug this into your Mac mini for a separate mic input and audio output: https://www.amazon.com/dp/B091N1RDD1/

Plug your headset into this for a separate mic output and audio input: https://www.amazon.com/dp/B091N52J6L/

With this setup, you can connect the mic output from the headset directly to the mic input on the Mac mini.

Then, you can connect the audio output on the Mac mini to your mixer and then plug the headset’s audio input to the mixer.