Same issue here, different mic. I suspect this has to do with Microsoft Co-Pilot components which were included in this update. I can not yet confirm. Even happens when I sign into OS after having locked the computer. Like others have said, seems to trigger when sound events happen. I have tried enable/disable/update drivers and enable/disable device in Control Panel. Have not yet found a solution. Event log is not clear. I can confirm this issue does not happen on another computer (same make and model) without update 24H2. I purposely waited until Feb. to install the update hoping that the bugs would have been worked out (see other issues with previous updates that were buggy for weeks before patching).
Microsoft, you are in violation of the HIPPA act in the United States by allowing the mic to randomly turn on. Might be time for a class action lawsuit (times the number of Win11 24H users)!