mmhmm will be "on" as long as it is the selected camera in the program you are using it with. If you would prefer to not use mmhmm for any given video call, navigate to your video conference platform's settings and select another webcam (i.e. unselect the mmhmm virtual camera). Read How do I turn mmhmm off for my next call? for more details.
This will have effectively turned mmhmm "off" until you select it again as your desired input camera. If you don't do this and mmhmm is not open, you will likely see a staticky black and white mmhmm logo.
If you deleted mmhmm and you still see the mmhmm virtual camera in your video conferencing app, follow this guide on how to fully uninstall mmhmm from your computer.