Researchers at the University of Wisconsin published this article which claims that
all of the apps they tested occasionally gather raw audio data while mute is activated, with one popular app gathering information and delivering data to its server at the same rate regardless of whether the microphone is muted or not.
Users of MeetingCaddy do not need to worry about being spied on because it uses a System(OS)-level muting function. This means that these popular apps that may be listening to you otherwise will NOT be able to do so when you are muting the microphone with MeetingCaddy.