How can I set system audio + microphone as the audio input for video conference software?

I am trying to set up my audio devices in a way that I can stream a mix of my voice (internal MacBook microphone) and the Mac's system audio via a video conference software. The software I am trying to use specifically is Microsoft Teams, but the same question could go for Skype or Zoom or any other video conference software that let's you select the audio input. I saw some online articles that suggested you create a "Multi-Output Device" in the Audio-MIDI-Setup software. But I tried that and I cannot get it to connect to Teams (i.e. I cannot select this Multi-Output Device as my "microphone" in Teams). Does anybody know how this can be achieved? Thanks!