Zoom first attempted to fix the bug in a December 5.9.1 update, as its release notes say Zoom “resolved an issue regarding the microphone light indicator being triggered when not in a meeting on macOS Monterey,” but it looks like this solution didn’t work for everyone.
“The Zoom client for macOS 5.9.3, released on January 25, 2022, fixed a bug involving the failure to properly terminate the microphone use post-meeting,” Zoom spokesperson Matt Nagel said in an emailed statement to The Verge. “Zoom has determined that this bug did not result in audio data being transmitted back to Zoom’s platform. As always, we recommend users make sure their Zoom client is updated to the latest version.”