In Windows, you can disable your microphone in your recording device settings, or switch your recording device to something other than the Bose headphones if your computer has other options in that dialog box. You can get to your recording devices by right-clicking the little speaker icon at the bottom right of your screen, and selecting recording devices in the pop-up.
The procedure is similar for Mac. You’ll need to either navigate to your sound settings in the settings pane, and then the recording tab…or use he Audio/MIDI controller app.
There’s no way to disable the sidetone in the headphones themselves, as Bose likes to keep things very simple. On a phone, the mic activates and deactivates automatically, but on a computer, the mic is always hot as long as that’s your default recording device, because that’s just the way computers operate. Hope that helps you out!