First, and it's a major lifeline as far as I'm concerned, remember that you can bring up the NVDA Commands Quick Reference in your web browser by hitting NVDA+N,H,Q. The vast majority of "the commonly used features or settings" will be found in that document, and Audio Ducking is one of them.
The keyboard shortcut for Audio Ducking is NVDA+SHIFT+D (regardless of whether you're using Desktop or Laptop keyboard layout). It is a "circular toggle" that allows you to choose either off or one of two other conditions under which ducking will occur.
Brian - Windows 10, 64-Bit, Version 21H1, Build 19043
I do not understand why some seek to separate a person from their actions. The self is composed of an individual’s thoughts, actions, and expression, which are contained in and actuated by the body. What you do and say is the clearest indicator of who you are.
~ Brian Vogel