There are so many different short key combinations in use in Windows 10 that it is difficult to select one to turn the Dragon NaturallySpeaking microphone on and off that doesn’t conflict with something else.
The default for Dragon is the numerical keypad key “+”, but my laptop does not have a numerical keypad. I have chosen instead to use “control-q” as the hotkey to turn on or off the microphone. This does not seem to conflict with anything else.
I have also remapped one of the mouse buttons to send “control-q” when pressed. I use an Evoluent vertical mouse which has a number of mouse buttons that can be configured to send keystrokes.