Go into the Preferences, Video Systems (last item), uncheck "Automatically discover nearby devices"
The default behavior of Webex is to grab the microphone and keep it always-open looking for audio signals from Webex-compatible hardware.
I found this because I was bothered that even though I wasn't on a call Windows was telling me that Webex was actively using the Microphone, so I dug in. IIRC the post that guided me to this, on Apple devices with their earbuds it apparently also significantly degrades the sound due to some codec issue (or did in the past).
The default behavior of Webex is to grab the microphone and keep it always-open looking for audio signals from Webex-compatible hardware.
I found this because I was bothered that even though I wasn't on a call Windows was telling me that Webex was actively using the Microphone, so I dug in. IIRC the post that guided me to this, on Apple devices with their earbuds it apparently also significantly degrades the sound due to some codec issue (or did in the past).