Given that this has been happening for about three years and has already been escalated to Apple Tier 2, I am less interested in the usual “restart your Mac” or “check your microphone” suggestions.
The fact that Voice Control suddenly stops listening and a restart is required to get it working again suggests that something in the Voice Control or speech-recognition system may be getting stuck.
1 - One thing worth trying the next time it happens is to turn Voice Control off and back on under System Settings >> Accessibility >> Voice Control rather than restarting the entire Mac. Apple confirms that Voice Control can be stopped and resumed independently.
Turn Voice Control on or off on Mac
2 - I would also try manually selecting the iMac’s built-in microphone instead of leaving the setting at “Automatic.”
Apple specifically provides a microphone selection for Voice Control.
Customize Voice Control on Mac
3 - If you use AirPods, a headset, webcam, or any other audio device, it would be useful to see whether the problem occurs after switching between audio inputs.
4 - The next time Voice Control fails, I would avoid restarting immediately and check System Settings >> Sound >> Input to see whether the microphone is still registering your voice. If the input meter responds normally but Voice Control does nothing, that would be useful evidence for Tier 2 because it would suggest the microphone itself is working and the problem is somewhere in the Voice Control/speech-processing chain.
Apple’s troubleshooting page specifically recommends checking the selected input device and input level when speech is not being recognized.
Dictation on Mac doesn’t work as expected
5 - Another useful test is to temporarily turn Voice Control off and try ordinary macOS Dictation.
Apple notes that when Voice Control is enabled, Voice Control handles dictation and standard Dictation is not available.
Use Voice Control commands to interact with your Mac
6 - If ordinary Dictation continues to work while Voice Control has stopped, that would be another useful clue.
Since Apple Tier 2 is already involved, I would specifically ask them what diagnostic information they want captured while Voice Control is actually broken, before rebooting.
A restart may clear the problem but also destroy the state that could help identify what is failing.
I would ask whether there is an Apple-supported way to restart the relevant speech/Voice Control service without restarting the entire Mac.
Apple's current documentation that is most relevant is:
Use Voice Control commands on Mac
Customize Voice Control on Mac
Turn Voice Control on or off
If Dictation on Mac doesn’t work as expected
Change the sound input settings on Mac
Dictate messages and documents on Mac
7 - At this point, I would be documenting exactly what happens when the failure occurs rather than repeatedly rebooting.
In particular: whether the microphone still shows input, whether turning Voice Control off/on restores it, whether ordinary Dictation still works, and whether the failure is associated with sleep/wake or switching audio devices. Those observations could give Tier 2 considerably more useful information than another post-reboot diagnostic report.
