MacOS 15 Sequoia Accessibility Services Using Microphone

It would seem, the Voice Control in System Setting >> Accessibilities has been switched ON

The microphone is listening for your next spoken words

Use Voice Control commands to interact with your Mac

In my case, this computer does not have a Builtin Microphone

What’s in the menu bar on Mac?

Zoom, Team Meeting, Skype, SIRI etc

Excerpt from above link

Control Center

Click  in the menu bar to open Control Center, where you can access features you use often, such as AirDrop, Stage Manager, Screen Mirroring, Focus, and more. See Use Control Center.

Privacy indicators, which can be dots or arrows, are located to the right of Control Center. An orange dot  next to the Control Center icon  in the menu bar indicates the microphone on your Mac is in use; a green dot  indicates a camera is in use; a purple dot  indicates the system audio is being recorded; and an arrow  indicates your location is in use. Only one privacy indicator dot is shown at a time. For example, if both the microphone and a camera are in use, you only see a green dot. When you open Control Center, the top of the window may contain a field that shows which apps are using your microphone, location, camera, or system audio. You can click that field to open the Privacy window, which may have additional information (macOS 13.3 or later).