I have this very strange problem that dictation is not working on my laptop when its lid is closed and it is connected to an external monitor (Cinema display). It does work fine when I use the laptop standalone.
Also, when I go to System Preferences / Keyboard / Dictation, I can see the microphone showing input (level meter does up and down when I speak). It does not matter whether the audio input under the microphone is on "Display audio" or "Automatic", when I open any other app and start dictating, the little microphone does not show any sign of activity (i.e., input).
Even more funny is that Siri on the laptop works fine, even with closed laptop lid, i.e., it does recognize my speech commands.
I think, the real problem is that, somehow, with display microphone, something is blocking the audio input on the way to the dictation software.
Of course, I have googled and tried a few things (reboot, switch audio, etc.), to no avail. But I haven't found a problem description on the web that matches the problems symptoms I am experiencing.
Does anyone have an idea?
PS: I recently upgraded to Catalina (10.15.3). Before, under Mojave, dictation worked.