Macbook Pro 2021 16" the F5 voice button does not work

On the new (2021) Macbook Pro, the F5 special function ('fn+F5) is a microphone icon which by default is supposed to start the voice-to-text dictation function when the cursor is in a text entry widget. I cannot get this function button to work. When I bring up the keyboard viewer and press 'fn+F5', I see the microphone button highlight in the simulated keyboard; this tells me the problem is not a bad/broken key. Further, when I go into Dictation prefs and change the activation key to something else, say, "Press Command Twice", dictation pops up and works, no problem. This seems like a bug in the OS, e.g., some logic is trapping and squelching the 'fn+F5' key press event.